implement the logic to set tile priorities based on current matrix

cc/picture_layer_tiling_set.h

Index: cc/picture_layer_tiling_set.h
diff --git a/cc/picture_layer_tiling_set.h b/cc/picture_layer_tiling_set.h
index d302125b4a1f980357a26165e3ccaf552de3a8d5..903c643992322b8ef608534a2146b8deedb63dae 100644
--- a/cc/picture_layer_tiling_set.h
+++ b/cc/picture_layer_tiling_set.h
@@ -28,6 +28,11 @@ class CC_EXPORT PictureLayerTilingSet {
   void AddTiling(float contents_scale, gfx::Size tile_size);
   size_t num_tilings() const { return tilings_.size(); }
 
+  void UpdateTilePriorities(const gfx::Size& view_port,
+                            const gfx::Transform& last_transform,
+                            const gfx::Transform& current_transform,
+                            double time_delta);
+
   // For a given rect, iterates through tiles that can fill it.  If no
   // set of tiles with resources can fill the rect, then it will iterate
   // through null tiles with valid geometry_rect() until the rect is full.