Move LayerImpl's bounds_delta to property trees

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 552582225b09d357ebfec6f9a11946e21fe4d13a..13733cc92c4a760be633851ffd47653235c65c72 100644
--- a/cc/layers/layer_impl.h
+++ b/cc/layers/layer_impl.h
@@ -269,8 +269,12 @@ class CC_EXPORT LayerImpl {
   // Like bounds() but doesn't snap to int. Lossy on giant pages (e.g. millions
   // of pixels) due to use of single precision float.
   gfx::SizeF BoundsForScrolling() const;
-  void SetBoundsDelta(const gfx::Vector2dF& bounds_delta);
-  gfx::Vector2dF bounds_delta() const { return bounds_delta_; }
+
+  // Viewport bounds delta are used for viewport layers and accounts for changes
+  // in the viewport layers from browser controls and page scale factors. These
+  // deltas are only set on the active tree.
+  void SetViewportBoundsDelta(const gfx::Vector2dF& bounds_delta);
+  gfx::Vector2dF ViewportBoundsDelta() const;
 
   void SetCurrentScrollOffset(const gfx::ScrollOffset& scroll_offset);
   gfx::ScrollOffset CurrentScrollOffset() const;
@@ -471,8 +475,6 @@ class CC_EXPORT LayerImpl {
 
   std::unique_ptr<LayerImplTestProperties> test_properties_;
 
-  gfx::Vector2dF bounds_delta_;
-
   // Properties synchronized from the associated Layer.
   gfx::Size bounds_;
   int scroll_clip_layer_id_;