android webview: allow cc to fail hardware draw

cc/trees/layer_tree_impl.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_IMPL_H_
 #define CC_TREES_LAYER_TREE_IMPL_H_
 
 #include <map>
 #include <set>
 #include <string>
@@ skipping 257 matching lines @@
   // and the active tree's size is now out of date.
   bool ViewportSizeInvalid() const;
   void SetViewportSizeInvalid();
   void ResetViewportSizeInvalid();
 
   // Useful for debug assertions, probably shouldn't be used for anything else.
   Proxy* proxy() const;
 
   // Distribute the root scroll between outer and inner viewport scroll layer.
   // The outer viewport scroll layer scrolls first.
-  void DistributeRootScrollOffset(const gfx::ScrollOffset& root_offset);
+  bool DistributeRootScrollOffset(const gfx::ScrollOffset& root_offset);
 
   void ApplyScroll(LayerImpl* layer, ScrollState* scroll_state) {
     layer_tree_host_impl_->ApplyScroll(layer, scroll_state);
   }
 
   // Call this function when you expect there to be a swap buffer.
   // See swap_promise.h for how to use SwapPromise.
   //
   // A swap promise queued by QueueSwapPromise travels with the layer
   // information currently associated with the tree. For example, when
@@ skipping 211 matching lines @@
 
   scoped_ptr<PendingPageScaleAnimation> pending_page_scale_animation_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(LayerTreeImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_IMPL_H_