cc: Update picture pile on tiles to prevent memory leak

cc/tile.h

Index: cc/tile.h
diff --git a/cc/tile.h b/cc/tile.h
index 7d41e6a8cb9b2f83ea88a76af82e0982f0694c8a..dcb24e09dd840abd87d47ea5240f032e0048ba94 100644
--- a/cc/tile.h
+++ b/cc/tile.h
@@ -54,6 +54,10 @@ class CC_EXPORT Tile : public base::RefCounted<Tile> {
   float contents_scale() const { return contents_scale_; }
   gfx::Rect content_rect() const { return content_rect_; }
 
+  void set_picture_pile(scoped_refptr<PicturePileImpl> pile) {
+   picture_pile_ = pile;
+  }
+
  private:
   // Methods called by by tile manager.
   friend class TileManager;