Extract subpixel offsets from composited layer transforms when possible.

cc/layers/layer_impl.h

Index: cc/layers/layer_impl.h
diff --git a/cc/layers/layer_impl.h b/cc/layers/layer_impl.h
index a7b6b69c50b3447cf58e0c95039e457d4ef6b280..4abc7aac2475e93b41eeebd939f704806f910c71 100644
--- a/cc/layers/layer_impl.h
+++ b/cc/layers/layer_impl.h
@@ -469,6 +469,7 @@ class CC_EXPORT LayerImpl {
   bool double_sided() const { return double_sided_; }
 
   void SetTransform(const gfx::Transform& transform);
+  void SetSubpixelOffset(const gfx::Vector2dF& subpixel_offset) { subpixel_offset_ = subpixel_offset; }
   const gfx::Transform& transform() const { return transform_; }
   bool TransformIsAnimating() const;
   bool HasPotentiallyRunningTransformAnimation() const;
@@ -734,6 +735,8 @@ class CC_EXPORT LayerImpl {
   int sorting_context_id_;
 
   DrawMode current_draw_mode_;
+public:
+  gfx::Vector2dF subpixel_offset_;
 
  private:
   uint64_t element_id_;
@@ -766,6 +769,7 @@ class CC_EXPORT LayerImpl {
   // If true, the layer or one of its descendants has a touch handler.
   bool layer_or_descendant_has_touch_handler_;
 
+
   DISALLOW_COPY_AND_ASSIGN(LayerImpl);
 };