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

cc/layers/layer.h

Index: cc/layers/layer.h
diff --git a/cc/layers/layer.h b/cc/layers/layer.h
index 581271731c5ad90510b582bc335461e999073947..938ca5edb9c3ba323dafb6f8da06ed609e2f9c98 100644
--- a/cc/layers/layer.h
+++ b/cc/layers/layer.h
@@ -505,6 +505,12 @@ class CC_EXPORT Layer : public base::RefCounted<Layer> {
   // 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