cc: Fix invalidation problems in impl-side painting

cc/picture_layer_tiling.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_PICTURE_LAYER_TILING_H_
 #define CC_PICTURE_LAYER_TILING_H_
 
 #include "base/basictypes.h"
 #include "base/hash_tables.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 45 matching lines @@
     // regardless of the contents scale of the tiling.
     gfx::Rect geometry_rect() const;
     // Texture rect (in texels) for geometry_rect
     gfx::RectF texture_rect() const;
     gfx::Size texture_size() const;
 
     Tile* operator->() const { return current_tile_; }
     Tile* operator*() const { return current_tile_; }
 
     Iterator& operator++();
-    operator bool() const { return current_tile_; }
+    operator bool() const { return tile_j_ <= bottom_; }
 
    private:
     PictureLayerTiling* tiling_;
     gfx::Rect dest_rect_;
     float dest_to_content_scale_;
 
     Tile* current_tile_;
     gfx::Rect current_geometry_rect_;
     int tile_i_;
     int tile_j_;
@@ skipping 29 matching lines @@
   gfx::Size layer_bounds_;
   TileMap tiles_;
   TilingData tiling_data_;
 
   friend class Iterator;
 };
 
 }  // namespace cc
 
 #endif  // CC_PICTURE_LAYER_TILING_H_