--- a/gfx/layers/LayersLogging.h
+++ b/gfx/layers/LayersLogging.h
@@ -4,16 +4,17 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #ifndef GFX_LAYERSLOGGING_H
 #define GFX_LAYERSLOGGING_H
 
 #include "FrameMetrics.h"               // for FrameMetrics, etc
 #include "mozilla/gfx/Matrix.h"         // for Matrix4x4
 #include "mozilla/gfx/Point.h"          // for IntSize, etc
+#include "mozilla/gfx/TiledRegion.h"    // for TiledRegion
 #include "mozilla/gfx/Types.h"          // for SamplingFilter, SurfaceFormat
 #include "mozilla/layers/CompositorTypes.h"  // for TextureFlags
 #include "nsAString.h"
 #include "nsPrintfCString.h"            // for nsPrintfCString
 #include "nsRegion.h"                   // for nsRegion, nsIntRegion
 #include "nscore.h"                     // for nsACString, etc
 
 namespace mozilla {
@@ -105,16 +106,28 @@ AppendToString(std::stringstream& aStrea
     AppendToString(aStream, iter.Get());
     aStream << "; ";
   }
   aStream << ">";
 
   aStream << sfx;
 }
 
+template <typename T>
+void
+AppendToString(std::stringstream& aStream, const mozilla::gfx::TiledRegion<T>& r,
+               const char* pfx="", const char* sfx="")
+{
+  aStream << pfx;
+  AppendToString(aStream, r.GetRegion());
+  aStream << " (bounds=";
+  AppendToString(aStream, r.GetBounds());
+  aStream << ", covers=" << r.CoversBounds() << ")" << sfx;
+}
+
 void
 AppendToString(std::stringstream& aStream, const EventRegions& e,
                const char* pfx="", const char* sfx="");
 
 void
 AppendToString(std::stringstream& aStream, const ScrollMetadata& m,
                const char* pfx="", const char* sfx="");
 

--- a/gfx/src/TiledRegion.h
+++ b/gfx/src/TiledRegion.h
@@ -131,16 +131,17 @@ public:
   void SetEmpty()
   {
     mBounds.SetEmpty();
     mImpl.Clear();
     mCoversBounds = false;
   }
 
   RectT GetBounds() const { return mBounds; }
+  bool CoversBounds() const { return mCoversBounds; }
 
   bool Intersects(const RectT& aRect) const
   {
     if (!mBounds.Intersects(aRect)) {
       return false;
     }
     if (mCoversBounds) {
       return true;