cc: Disallow scroll offset animations when impl-scrolling isn't supported

cc/trees/thread_proxy.cc

 // Copyright 2011 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.
 
 #include "cc/trees/thread_proxy.h"
 
 #include <algorithm>
 #include <string>
 
 #include "base/auto_reset.h"
@@ skipping 644 matching lines @@
   completion.Wait();
 }
 
 void ThreadProxy::ForceSerializeOnSwapBuffersOnImplThread(
     CompletionEvent* completion) {
   if (impl().layer_tree_host_impl->renderer())
     impl().layer_tree_host_impl->renderer()->DoNoOp();
   completion->Signal();
 }
 
+bool ThreadProxy::SupportsImplScrolling() const {
+  return true;
+}
+
 void ThreadProxy::SetDebugState(const LayerTreeDebugState& debug_state) {
   Proxy::ImplThreadTaskRunner()->PostTask(
       FROM_HERE,
       base::Bind(&ThreadProxy::SetDebugStateOnImplThread,
                  impl_thread_weak_ptr_,
                  debug_state));
 }
 
 void ThreadProxy::SetDebugStateOnImplThread(
     const LayerTreeDebugState& debug_state) {
@@ skipping 761 matching lines @@
 
   impl().timing_history.DidActivatePendingTree();
 }
 
 void ThreadProxy::DidManageTiles() {
   DCHECK(IsImplThread());
   impl().scheduler->DidManageTiles();
 }
 
 }  // namespace cc