Animated scroll shouldn't require main-frame for OOPIFs.

cc/trees/layer_tree_host_client.h

 // Copyright 2012 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_TREES_LAYER_TREE_HOST_CLIENT_H_
 #define CC_TREES_LAYER_TREE_HOST_CLIENT_H_
 
 #include <memory>
 
 #include "base/memory/ref_counted.h"
@@ skipping 40 matching lines @@
   // either DidFailToInitializeCompositorFrameSink or
   // DidInitializeCompositorFrameSink being called.
   virtual void RequestNewCompositorFrameSink() = 0;
   virtual void DidInitializeCompositorFrameSink() = 0;
   virtual void DidFailToInitializeCompositorFrameSink() = 0;
   virtual void WillCommit() = 0;
   virtual void DidCommit() = 0;
   virtual void DidCommitAndDrawFrame() = 0;
   virtual void DidReceiveCompositorFrameAck() = 0;
   virtual void DidCompletePageScaleAnimation() = 0;
+  // The only time a subframe ever gets its own LayerTree is when the subframe
+  // renders in a different process its ancestors; this returns true in
+  // that case.
+  virtual bool IsForSubframe() = 0;
 
  protected:
   virtual ~LayerTreeHostClient() {}
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_HOST_CLIENT_H_