cc: Move SyncedScrollOffset to scroll tree

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 fdc5261e673b99ef9b558dfd331a3dacaf40688b..2752c16914443455045bca754c1fd398602c2bd4 100644
--- a/cc/layers/layer_impl.h
+++ b/cc/layers/layer_impl.h
@@ -83,7 +83,6 @@ class CC_EXPORT LayerImpl : public LayerAnimationValueObserver,
                             public LayerAnimationValueProvider,
                             public AnimationDelegate {
  public:
-  typedef SyncedProperty<AdditionGroup<gfx::ScrollOffset>> SyncedScrollOffset;
   typedef LayerImplList RenderSurfaceListType;
   typedef LayerImplList LayerListType;
   typedef RenderSurfaceImpl RenderSurfaceType;
@@ -462,17 +461,21 @@ class CC_EXPORT LayerImpl : public LayerAnimationValueObserver,
   gfx::Vector2dF bounds_delta() const { return bounds_delta_; }
 
   void SetCurrentScrollOffset(const gfx::ScrollOffset& scroll_offset);
+  // must only be called by tests when updating scroll offset of a single layer,
+  // the standard process to update scroll offsets is to call
+  // ScrollTree::UpdateScrollOffsetMap() which updates scroll offsets of all
+  // layers.
   void PushScrollOffsetFromMainThread(const gfx::ScrollOffset& scroll_offset);
-  // This method is similar to PushScrollOffsetFromMainThread but will cause the
-  // scroll offset given to clobber any scroll changes on the active tree in the
-  // time until this value is pushed to the active tree.
-  void PushScrollOffsetFromMainThreadAndClobberActiveValue(
-      const gfx::ScrollOffset& scroll_offset);
-  gfx::ScrollOffset PullDeltaForMainThread();
+
   gfx::ScrollOffset CurrentScrollOffset() const;
   gfx::ScrollOffset BaseScrollOffset() const;
   gfx::Vector2dF ScrollDelta() const;
   void SetScrollDelta(const gfx::Vector2dF& delta);
+  // This is a mirror function of Layer::scroll_offset, which is supposed to be
+  // called only by PropertyTreeBuilder
+  gfx::ScrollOffset scroll_offset() const {
+    return synced_scroll_offset()->PendingBase();
+  }
 
   gfx::ScrollOffset MaxScrollOffset() const;
   gfx::ScrollOffset ClampScrollOffsetToLimits(gfx::ScrollOffset offset) const;
@@ -506,8 +509,6 @@ class CC_EXPORT LayerImpl : public LayerAnimationValueObserver,
 
   bool user_scrollable(ScrollbarOrientation orientation) const;
 
-  void ApplySentScrollDeltasFromAbortedCommit();
-
   void set_main_thread_scrolling_reasons(
       uint32_t main_thread_scrolling_reasons);
   uint32_t main_thread_scrolling_reasons() const {
@@ -636,7 +637,8 @@ class CC_EXPORT LayerImpl : public LayerAnimationValueObserver,
   }
   void GatherFrameTimingRequestIds(std::vector<int64_t>* request_ids);
 
-  SyncedScrollOffset* synced_scroll_offset() { return scroll_offset_.get(); }
+  const SyncedScrollOffset* synced_scroll_offset() const;
+  SyncedScrollOffset* synced_scroll_offset();
 
   // Get the correct invalidation region instead of conservative Rect
   // for layers that provide it.
@@ -686,6 +688,7 @@ class CC_EXPORT LayerImpl : public LayerAnimationValueObserver,
   }
 
   void NoteLayerPropertyChanged();
+  void DidUpdateScrollOffset();
 
   void PushLayerPropertyChangedForSubtree();
 
@@ -719,8 +722,6 @@ class CC_EXPORT LayerImpl : public LayerAnimationValueObserver,
  private:
   void ValidateQuadResourcesInternal(DrawQuad* quad) const;
 
-  void PushScrollOffset(const gfx::ScrollOffset* scroll_offset);
-  void DidUpdateScrollOffset();
   void NoteLayerPropertyChangedForDescendantsInternal();
   void PushLayerPropertyChangedForSubtreeInternal();
 
@@ -750,8 +751,6 @@ class CC_EXPORT LayerImpl : public LayerAnimationValueObserver,
   int layer_id_;
   LayerTreeImpl* layer_tree_impl_;
 
-  // Properties dynamically changeable on active tree.
-  scoped_refptr<SyncedScrollOffset> scroll_offset_;
   gfx::Vector2dF bounds_delta_;
 
   // Properties synchronized from the associated Layer.