--- a/servo/components/style/Cargo.toml
+++ b/servo/components/style/Cargo.toml
@@ -24,17 +24,17 @@ servo = ["serde", "heapsize", "heapsize_
 
          # FIXME: Uncomment when https://github.com/servo/servo/pull/16953 has landed:
          #"arrayvec/use_union"
 
          "servo_url"]
 gecko_debug = ["nsstring_vendor/gecko_debug"]
 
 [dependencies]
-app_units = "0.5.3"
+app_units = "0.5.5"
 arrayvec = "0.3.20"
 arraydeque = "0.2.3"
 atomic_refcell = "0.1"
 bitflags = "0.7"
 bit-vec = "0.4.3"
 byteorder = "1.0"
 cfg-if = "0.1.0"
 cssparser = "0.20"

--- a/third_party/rust/app_units/.cargo-checksum.json
+++ b/third_party/rust/app_units/.cargo-checksum.json
@@ -1,1 +1,1 @@
-{"files":{".cargo-ok":"e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",".travis.yml":"6b96b2c6bfd7e1acef4b825a2813fc4277859eb9400a16800db8835c25e4087d","Cargo.toml":"1648e6342e3879aaf3add2a9341915ca1650037df830907dc1e2b768aa087036","README.md":"9f048d969f9f8333cdcdb892744cd0816e4f2922c8817fa5e9e07f9472fe1050","src/app_unit.rs":"7e75ca0ad78d26c6538029c7ddae650f7b76c2f7210735e6da6e52920494fdb4","src/lib.rs":"2df7d863c47d8b22f9af66caeafa87e6a206ee713a8aeaa55c5a80a42a92513b"},"package":"7ff4f3fe57393a150b39b026b6f6f4b9a6c4f49b52d0a4e2d61d08d926358438"}
\ No newline at end of file
+{"files":{".cargo-ok":"e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",".travis.yml":"6b96b2c6bfd7e1acef4b825a2813fc4277859eb9400a16800db8835c25e4087d","Cargo.toml":"062e80e89fe612fbe4a8e03ef2e40f8b2b2790ebdbb746bb8e51ac10ae5640e0","README.md":"9f048d969f9f8333cdcdb892744cd0816e4f2922c8817fa5e9e07f9472fe1050","src/app_unit.rs":"65c5ae98e48298ba3c5380b529f1395d39a09259bd18de3833fa12a98344e492","src/lib.rs":"2df7d863c47d8b22f9af66caeafa87e6a206ee713a8aeaa55c5a80a42a92513b"},"package":"7eb1573f29213263e6016754100e0ae875049d3692dfe6764834c2d7957ca94c"}
\ No newline at end of file

--- a/third_party/rust/app_units/Cargo.toml
+++ b/third_party/rust/app_units/Cargo.toml
@@ -7,25 +7,25 @@
 #
 # If you believe there's an error in this file please file an
 # issue against the rust-lang/cargo repository. If you're
 # editing this file be aware that the upstream Cargo.toml
 # will likely look very different (and much more reasonable)
 
 [package]
 name = "app_units"
-version = "0.5.3"
+version = "0.5.5"
 authors = ["The Servo Project Developers"]
 description = "Servo app units type (Au)"
 documentation = "http://doc.servo.org/app_units/"
 license = "MPL-2.0"
 repository = "https://github.com/servo/app_units"
-[dependencies.serde]
-version = "1.0"
-
 [dependencies.num-traits]
 version = "0.1.32"
 
-[dependencies.rustc-serialize]
-version = "0.3"
+[dependencies.serde]
+version = "1.0"
 
 [dependencies.heapsize]
 version = ">=0.3, < 0.5"
+
+[dependencies.rustc-serialize]
+version = "0.3"

--- a/third_party/rust/app_units/src/app_unit.rs
+++ b/third_party/rust/app_units/src/app_unit.rs
@@ -190,21 +190,28 @@ impl Au {
     #[inline]
     fn clamp_self(&mut self) {
         *self = self.clamp()
     }
 
     #[inline]
     pub fn scale_by(self, factor: f32) -> Au {
         let new_float = ((self.0 as f64) * factor as f64).round();
-        Au::clamp_from_f64_au(new_float)
+        Au::from_f64_au(new_float)
     }
 
     #[inline]
-    fn clamp_from_f64_au(float: f64) -> Self {
+    /// Scale, but round down (useful for viewport-relative units)
+    pub fn scale_by_trunc(self, factor: f32) -> Au {
+        let new_float = ((self.0 as f64) * factor as f64).floor();
+        Au::from_f64_au(new_float)
+    }
+
+    #[inline]
+    pub fn from_f64_au(float: f64) -> Self {
         // We *must* operate in f64. f32 isn't precise enough
         // to handle MAX_AU
         Au(float.min(MAX_AU.0 as f64)
                 .max(MIN_AU.0 as f64)
             as i32)
     }
 
     #[inline]
@@ -242,23 +249,23 @@ impl Au {
     #[inline]
     pub fn to_f64_px(self) -> f64 {
         (self.0 as f64) / (AU_PER_PX as f64)
     }
 
     #[inline]
     pub fn from_f32_px(px: f32) -> Au {
         let float = (px * AU_PER_PX as f32).round();
-        Au::clamp_from_f64_au(float as f64)
+        Au::from_f64_au(float as f64)
     }
 
     #[inline]
     pub fn from_f64_px(px: f64) -> Au {
         let float = (px * AU_PER_PX as f64).round();
-        Au::clamp_from_f64_au(float)
+        Au::from_f64_au(float)
     }
 
     #[inline]
     pub fn abs(self) -> Self {
         Au(self.0.abs())
     }
 }
 
@@ -298,16 +305,17 @@ fn saturate() {
     assert_eq!(-half * -10, MAX_AU);
 }
 
 #[test]
 fn scale() {
     assert_eq!(Au(12).scale_by(1.5), Au(18));
     assert_eq!(Au(12).scale_by(1.7), Au(20));
     assert_eq!(Au(12).scale_by(1.8), Au(22));
+    assert_eq!(Au(12).scale_by_trunc(1.8), Au(21));
 }
 
 #[test]
 fn abs() {
     assert_eq!(Au(-10).abs(), Au(10));
 }
 
 #[test]

--- a/toolkit/library/gtest/rust/Cargo.lock
+++ b/toolkit/library/gtest/rust/Cargo.lock
@@ -17,17 +17,17 @@ dependencies = [
 
 [[package]]
 name = "ansi_term"
 version = "0.9.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "app_units"
-version = "0.5.3"
+version = "0.5.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "heapsize 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "num-traits 0.1.37 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc-serialize 0.3.22 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde 1.0.8 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -1198,17 +1198,17 @@ source = "registry+https://github.com/ru
 name = "strsim"
 version = "0.6.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "style"
 version = "0.0.1"
 dependencies = [
- "app_units 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "app_units 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "arraydeque 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "arrayvec 0.3.23 (registry+https://github.com/rust-lang/crates.io-index)",
  "atomic_refcell 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "bindgen 0.29.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "bit-vec 0.4.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "bitflags 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "byteorder 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "cfg-if 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1254,17 +1254,17 @@ dependencies = [
  "syn 0.11.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "synstructure 0.5.2 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "style_traits"
 version = "0.0.1"
 dependencies = [
- "app_units 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "app_units 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "bitflags 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "cssparser 0.20.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "euclid 0.15.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "selectors 0.19.0",
 ]
 
 [[package]]
 name = "syn"
@@ -1463,17 +1463,17 @@ dependencies = [
  "same-file 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "winapi 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "webrender"
 version = "0.50.0"
 dependencies = [
- "app_units 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "app_units 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "bincode 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "bit-set 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "bitflags 0.9.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "byteorder 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "core-graphics 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "core-text 6.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "dwrote 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "euclid 0.15.1 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1490,34 +1490,34 @@ dependencies = [
  "time 0.1.36 (registry+https://github.com/rust-lang/crates.io-index)",
  "webrender_api 0.50.0",
 ]
 
 [[package]]
 name = "webrender_api"
 version = "0.50.0"
 dependencies = [
- "app_units 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "app_units 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "bincode 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "byteorder 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "core-foundation 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "core-graphics 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "dwrote 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "euclid 0.15.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "fxhash 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "heapsize 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde 1.0.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "time 0.1.36 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "webrender_bindings"
 version = "0.1.0"
 dependencies = [
- "app_units 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "app_units 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "bincode 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "euclid 0.15.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "gleam 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "rayon 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "thread_profiler 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "webrender 0.50.0",
  "webrender_api 0.50.0",
 ]
@@ -1547,17 +1547,17 @@ version = "0.3.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "bitflags 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [metadata]
 "checksum aho-corasick 0.6.2 (registry+https://github.com/rust-lang/crates.io-index)" = "0638fd549427caa90c499814196d1b9e3725eb4d15d7339d6de073a680ed0ca2"
 "checksum ansi_term 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)" = "23ac7c30002a5accbf7e8987d0632fa6de155b7c3d39d0067317a391e00a2ef6"
-"checksum app_units 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)" = "7ff4f3fe57393a150b39b026b6f6f4b9a6c4f49b52d0a4e2d61d08d926358438"
+"checksum app_units 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)" = "7eb1573f29213263e6016754100e0ae875049d3692dfe6764834c2d7957ca94c"
 "checksum arraydeque 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)" = "96e774cadb24c2245225280c6799793f9802b918a58a79615e9490607489a717"
 "checksum arrayvec 0.3.23 (registry+https://github.com/rust-lang/crates.io-index)" = "699e63a93b79d717e8c3b5eb1b28b7780d0d6d9e59a72eb769291c83b0c8dc67"
 "checksum aster 0.41.0 (registry+https://github.com/rust-lang/crates.io-index)" = "4ccfdf7355d9db158df68f976ed030ab0f6578af811f5a7bb6dcf221ec24e0e0"
 "checksum atomic_refcell 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "fb2dcb6e6d35f20276943cc04bb98e538b348d525a04ac79c10021561d202f21"
 "checksum atty 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)" = "d912da0db7fa85514874458ca3651fe2cddace8d0b0505571dbdcd41ab490159"
 "checksum backtrace 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)" = "72f9b4182546f4b04ebc4ab7f84948953a118bd6021a1b6a6c909e3e94f6be76"
 "checksum backtrace-sys 0.1.10 (registry+https://github.com/rust-lang/crates.io-index)" = "d192fd129132fbc97497c1f2ec2c2c5174e376b95f535199ef4fe0a293d33842"
 "checksum binary-space-partition 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)" = "88ceb0d16c4fd0e42876e298d7d3ce3780dd9ebdcbe4199816a32c77e08597ff"

--- a/toolkit/library/rust/Cargo.lock
+++ b/toolkit/library/rust/Cargo.lock
@@ -15,17 +15,17 @@ dependencies = [
 
 [[package]]
 name = "ansi_term"
 version = "0.9.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "app_units"
-version = "0.5.3"
+version = "0.5.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "heapsize 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "num-traits 0.1.37 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc-serialize 0.3.22 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde 1.0.8 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -1185,17 +1185,17 @@ source = "registry+https://github.com/ru
 name = "strsim"
 version = "0.6.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "style"
 version = "0.0.1"
 dependencies = [
- "app_units 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "app_units 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "arraydeque 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "arrayvec 0.3.23 (registry+https://github.com/rust-lang/crates.io-index)",
  "atomic_refcell 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "bindgen 0.29.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "bit-vec 0.4.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "bitflags 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "byteorder 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "cfg-if 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1241,17 +1241,17 @@ dependencies = [
  "syn 0.11.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "synstructure 0.5.2 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "style_traits"
 version = "0.0.1"
 dependencies = [
- "app_units 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "app_units 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "bitflags 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "cssparser 0.20.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "euclid 0.15.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "selectors 0.19.0",
 ]
 
 [[package]]
 name = "syn"
@@ -1450,17 +1450,17 @@ dependencies = [
  "same-file 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "winapi 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "webrender"
 version = "0.50.0"
 dependencies = [
- "app_units 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "app_units 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "bincode 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "bit-set 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "bitflags 0.9.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "byteorder 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "core-graphics 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "core-text 6.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "dwrote 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "euclid 0.15.1 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1477,34 +1477,34 @@ dependencies = [
  "time 0.1.36 (registry+https://github.com/rust-lang/crates.io-index)",
  "webrender_api 0.50.0",
 ]
 
 [[package]]
 name = "webrender_api"
 version = "0.50.0"
 dependencies = [
- "app_units 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "app_units 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "bincode 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "byteorder 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "core-foundation 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "core-graphics 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "dwrote 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "euclid 0.15.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "fxhash 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "heapsize 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde 1.0.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "time 0.1.36 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "webrender_bindings"
 version = "0.1.0"
 dependencies = [
- "app_units 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "app_units 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "bincode 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "euclid 0.15.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "gleam 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "rayon 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "thread_profiler 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "webrender 0.50.0",
  "webrender_api 0.50.0",
 ]
@@ -1534,17 +1534,17 @@ version = "0.3.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "bitflags 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [metadata]
 "checksum aho-corasick 0.6.2 (registry+https://github.com/rust-lang/crates.io-index)" = "0638fd549427caa90c499814196d1b9e3725eb4d15d7339d6de073a680ed0ca2"
 "checksum ansi_term 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)" = "23ac7c30002a5accbf7e8987d0632fa6de155b7c3d39d0067317a391e00a2ef6"
-"checksum app_units 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)" = "7ff4f3fe57393a150b39b026b6f6f4b9a6c4f49b52d0a4e2d61d08d926358438"
+"checksum app_units 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)" = "7eb1573f29213263e6016754100e0ae875049d3692dfe6764834c2d7957ca94c"
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