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

cc/trees/proxy.h

 // 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.
 
 #ifndef CC_TREES_PROXY_H_
 #define CC_TREES_PROXY_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 71 matching lines @@
   virtual void Start() = 0;
   virtual void Stop() = 0;   // Must be called before deleting the proxy.
 
   // Forces 3D commands on all contexts to wait for all previous SwapBuffers
   // to finish before executing in the GPU process.
   virtual void ForceSerializeOnSwapBuffers() = 0;
 
   // Maximum number of sub-region texture updates supported for each commit.
   virtual size_t MaxPartialTextureUpdates() const = 0;
 
+  virtual bool SupportsImplScrolling() const = 0;
+
   virtual scoped_ptr<base::Value> AsValue() const = 0;
 
   virtual void SetDebugState(const LayerTreeDebugState& debug_state) = 0;
 
   // Testing hooks
   virtual bool CommitPendingForTesting() = 0;
   virtual scoped_ptr<base::Value> SchedulerAsValueForTesting();
 
  protected:
   explicit Proxy(
@@ skipping 35 matching lines @@
   explicit DebugScopedSetMainThreadBlocked(Proxy* proxy) {}
   ~DebugScopedSetMainThreadBlocked() {}
  private:
   DISALLOW_COPY_AND_ASSIGN(DebugScopedSetMainThreadBlocked);
 };
 #endif
 
 }  // namespace cc
 
 #endif  // CC_TREES_PROXY_H_