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

cc/test/fake_picture_layer_tiling_client.cc

 // 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.
 
 #include "cc/test/fake_picture_layer_tiling_client.h"
 
 #include <limits>
 
 #include "cc/test/fake_picture_pile_impl.h"
 #include "cc/test/fake_tile_manager.h"
@@ skipping 59 matching lines @@
 
 int FakePictureLayerTilingClient::GetSkewportExtrapolationLimitInContentPixels()
     const {
   return skewport_extrapolation_limit_in_content_pixels_;
 }
 
 const Region* FakePictureLayerTilingClient::GetPendingInvalidation() {
   return &invalidation_;
 }
 
-const PictureLayerTiling* FakePictureLayerTilingClient::GetTwinTiling(
-      const PictureLayerTiling* tiling) const {
+const PictureLayerTiling*
+FakePictureLayerTilingClient::GetPendingOrActiveTwinTiling(
+    const PictureLayerTiling* tiling) const {
   return twin_tiling_;
 }
 
 PictureLayerTiling* FakePictureLayerTilingClient::GetRecycledTwinTiling(
     const PictureLayerTiling* tiling) {
   return recycled_twin_tiling_;
 }
 
 WhichTree FakePictureLayerTilingClient::GetTree() const {
   return tree_;
 }
 
 bool FakePictureLayerTilingClient::RequiresHighResToDraw() const {
   return false;
 }
 
 }  // namespace cc