cc: Always keep the PictureLayerImpl::twin_layer_ pointer valid.

cc/trees/layer_tree_impl.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/layer_tree_impl.h"
 
 #include <limits>
 #include <set>
 
 #include "base/debug/trace_event.h"
@@ skipping 732 matching lines @@
   return tree->LayerById(id);
 }
 
 LayerImpl* LayerTreeImpl::FindPendingTreeLayerById(int id) {
   LayerTreeImpl* tree = layer_tree_host_impl_->pending_tree();
   if (!tree)
     return NULL;
   return tree->LayerById(id);
 }
 
-LayerImpl* LayerTreeImpl::FindRecycleTreeLayerById(int id) {
-  LayerTreeImpl* tree = layer_tree_host_impl_->recycle_tree();
-  if (!tree)
-    return NULL;
-  return tree->LayerById(id);
-}
-
 bool LayerTreeImpl::PinchGestureActive() const {
   return layer_tree_host_impl_->pinch_gesture_active();
 }
 
 BeginFrameArgs LayerTreeImpl::CurrentBeginFrameArgs() const {
   return layer_tree_host_impl_->CurrentBeginFrameArgs();
 }
 
 base::TimeDelta LayerTreeImpl::begin_impl_frame_interval() const {
   return layer_tree_host_impl_->begin_impl_frame_interval();
@@ skipping 752 matching lines @@
                                   page_scale,
                                   duration.InSecondsF());
   }
 }
 
 scoped_ptr<PageScaleAnimation> LayerTreeImpl::TakePageScaleAnimation() {
   return page_scale_animation_.Pass();
 }
 
 }  // namespace cc