Rewrite Layer::SetScrollOffset{FromImplSide} property tree fast-path

cc/layers/layer.h

 // Copyright 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_LAYERS_LAYER_H_
 #define CC_LAYERS_LAYER_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 487 matching lines @@
   void RemoveFromClipTree();
 
   // When we detach or attach layer to new LayerTreeHost, all property trees'
   // indices becomes invalid.
   void InvalidatePropertyTreesIndices();
 
   // This is set whenever a property changed on layer that affects whether this
   // layer should own a property tree node or not.
   void SetPropertyTreesNeedRebuild();
 
+  // Fast-path for |SetScrollOffset| and |SetScrollOffsetFromImplSide| to
+  // directly update scroll offset values in the property tree without needing a
+  // full property tree update. If property trees do not exist yet, ensures
+  // they are marked as needing to be rebuilt.
+  void UpdateScrollOffset(const gfx::ScrollOffset&);
+
   // Encapsulates all data, callbacks or interfaces received from the embedder.
   // TODO(khushalsagar): This is only valid when PropertyTrees are built
   // internally in cc. Update this for the SPv2 path where blink generates
   // PropertyTrees.
   struct Inputs {
     explicit Inputs(int layer_id);
     ~Inputs();
 
     int layer_id;
 
@@ skipping 111 matching lines @@
   // These all act like draw properties, so don't need push properties.
   gfx::Rect visible_layer_rect_;
   size_t num_unclipped_descendants_;
 
   DISALLOW_COPY_AND_ASSIGN(Layer);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_LAYER_H_