cc: Clear tile priorities when tiling is reset.

cc/resources/picture_layer_tiling.h

Index: cc/resources/picture_layer_tiling.h
diff --git a/cc/resources/picture_layer_tiling.h b/cc/resources/picture_layer_tiling.h
index 5aaadf13d19f3e3230da0b5dcdc0215141b21736..a6c945d75e53691d24e17d72043393ece8eb0242 100644
--- a/cc/resources/picture_layer_tiling.h
+++ b/cc/resources/picture_layer_tiling.h
@@ -169,6 +169,13 @@ class CC_EXPORT PictureLayerTiling {
     return all_tiles;
   }
 
+  std::vector<scoped_refptr<Tile> > AllRefTilesForTesting() const {
+    std::vector<scoped_refptr<Tile> > all_tiles;
+    for (TileMap::const_iterator it = tiles_.begin(); it != tiles_.end(); ++it)
+      all_tiles.push_back(it->second);
+    return all_tiles;
+  }
+
   const gfx::Rect& GetCurrentVisibleRectForTesting() const {
     return current_visible_rect_;
   }