--- a/layout/base/Units.h
+++ b/layout/base/Units.h
@@ -23,23 +23,25 @@ namespace mozilla {
 
 template <typename T>
 struct IsPixel : FalseType {};
 
 // See struct declaration for a description of each unit type.
 struct CSSPixel;
 struct LayoutDevicePixel;
 struct LayerPixel;
+struct CSSTransformedLayerPixel;
 struct RenderTargetPixel;
 struct ScreenPixel;
 struct ParentLayerPixel;
 
 template<> struct IsPixel<CSSPixel>          : TrueType {};
 template<> struct IsPixel<LayoutDevicePixel> : TrueType {};
 template<> struct IsPixel<LayerPixel>        : TrueType {};
+template<> struct IsPixel<CSSTransformedLayerPixel> : TrueType {};
 template<> struct IsPixel<RenderTargetPixel> : TrueType {};
 template<> struct IsPixel<ScreenPixel>       : TrueType {};
 template<> struct IsPixel<ParentLayerPixel>  : TrueType {};
 
 typedef gfx::CoordTyped<CSSPixel> CSSCoord;
 typedef gfx::IntCoordTyped<CSSPixel> CSSIntCoord;
 typedef gfx::PointTyped<CSSPixel> CSSPoint;
 typedef gfx::IntPointTyped<CSSPixel> CSSIntPoint;
@@ -70,16 +72,28 @@ typedef gfx::IntPointTyped<LayerPixel> L
 typedef gfx::SizeTyped<LayerPixel> LayerSize;
 typedef gfx::IntSizeTyped<LayerPixel> LayerIntSize;
 typedef gfx::RectTyped<LayerPixel> LayerRect;
 typedef gfx::IntRectTyped<LayerPixel> LayerIntRect;
 typedef gfx::MarginTyped<LayerPixel> LayerMargin;
 typedef gfx::IntMarginTyped<LayerPixel> LayerIntMargin;
 typedef gfx::IntRegionTyped<LayerPixel> LayerIntRegion;
 
+typedef gfx::CoordTyped<CSSTransformedLayerPixel> CSSTransformedLayerCoord;
+typedef gfx::IntCoordTyped<CSSTransformedLayerPixel> CSSTransformedLayerIntCoord;
+typedef gfx::PointTyped<CSSTransformedLayerPixel> CSSTransformedLayerPoint;
+typedef gfx::IntPointTyped<CSSTransformedLayerPixel> CSSTransformedLayerIntPoint;
+typedef gfx::SizeTyped<CSSTransformedLayerPixel> CSSTransformedLayerSize;
+typedef gfx::IntSizeTyped<CSSTransformedLayerPixel> CSSTransformedLayerIntSize;
+typedef gfx::RectTyped<CSSTransformedLayerPixel> CSSTransformedLayerRect;
+typedef gfx::IntRectTyped<CSSTransformedLayerPixel> CSSTransformedLayerIntRect;
+typedef gfx::MarginTyped<CSSTransformedLayerPixel> CSSTransformedLayerMargin;
+typedef gfx::IntMarginTyped<CSSTransformedLayerPixel> CSSTransformedLayerIntMargin;
+typedef gfx::IntRegionTyped<CSSTransformedLayerPixel> CSSTransformedLayerIntRegion;
+
 typedef gfx::PointTyped<RenderTargetPixel> RenderTargetPoint;
 typedef gfx::IntPointTyped<RenderTargetPixel> RenderTargetIntPoint;
 typedef gfx::SizeTyped<RenderTargetPixel> RenderTargetSize;
 typedef gfx::IntSizeTyped<RenderTargetPixel> RenderTargetIntSize;
 typedef gfx::RectTyped<RenderTargetPixel> RenderTargetRect;
 typedef gfx::IntRectTyped<RenderTargetPixel> RenderTargetIntRect;
 typedef gfx::MarginTyped<RenderTargetPixel> RenderTargetMargin;
 typedef gfx::IntMarginTyped<RenderTargetPixel> RenderTargetIntMargin;
@@ -320,16 +334,26 @@ struct LayoutDevicePixel {
  * 2) the "full zoom" (see nsPresContext::SetFullZoom)
  * 3) the "widget scale" (see nsIWidget::GetDefaultScale)
  * 4) rasterizing at a different scale in the presence of some CSS transforms
  */
 struct LayerPixel {
 };
 
 /*
+ * This is Layer coordinates with the Layer's CSS transform applied.
+ * It can be thought of as intermediate between LayerPixel and
+ * ParentLayerPixel, as further applying async transforms to this
+ * yields ParentLayerPixels.
+ */
+struct CSSTransformedLayerPixel {
+
+};
+
+/*
  * Layers are always composited to a render target. This unit
  * represents one pixel in the render target. Note that for the
  * root render target RenderTargetPixel == ScreenPixel. Also
  * any ContainerLayer providing an intermediate surface will
  * have RenderTargetPixel == LayerPixel.
  */
 struct RenderTargetPixel {
 };