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

cc/test/fake_picture_layer_tiling_client.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_TEST_FAKE_PICTURE_LAYER_TILING_CLIENT_H_
 #define CC_TEST_FAKE_PICTURE_LAYER_TILING_CLIENT_H_
 
 #include "cc/resources/picture_layer_tiling.h"
 #include "cc/resources/picture_pile_impl.h"
 #include "cc/resources/tile.h"
@@ skipping 16 matching lines @@
   gfx::Size CalculateTileSize(const gfx::Size& content_bounds) const override;
   size_t GetMaxTilesForInterestArea() const override;
   float GetSkewportTargetTimeInSeconds() const override;
   int GetSkewportExtrapolationLimitInContentPixels() const override;
   bool RequiresHighResToDraw() const override;
 
   void SetTileSize(const gfx::Size& tile_size);
   gfx::Size TileSize() const { return tile_size_; }
 
   const Region* GetPendingInvalidation() override;
-  const PictureLayerTiling* GetTwinTiling(
+  const PictureLayerTiling* GetPendingOrActiveTwinTiling(
       const PictureLayerTiling* tiling) const override;
   PictureLayerTiling* GetRecycledTwinTiling(
       const PictureLayerTiling* tiling) override;
   WhichTree GetTree() const override;
 
   void set_twin_tiling(PictureLayerTiling* tiling) { twin_tiling_ = tiling; }
   void set_recycled_twin_tiling(PictureLayerTiling* tiling) {
     recycled_twin_tiling_ = tiling;
   }
   void set_text_rect(const gfx::Rect& rect) { text_rect_ = rect; }
@@ skipping 27 matching lines @@
   Region invalidation_;
   size_t max_tiles_for_interest_area_;
   float skewport_target_time_in_seconds_;
   int skewport_extrapolation_limit_in_content_pixels_;
   WhichTree tree_;
 };
 
 }  // namespace cc
 
 #endif  // CC_TEST_FAKE_PICTURE_LAYER_TILING_CLIENT_H_