cc: Separate tiling set functionality into explicit separate functions.

cc/resources/picture_layer_tiling.cc

Index: cc/resources/picture_layer_tiling.cc
diff --git a/cc/resources/picture_layer_tiling.cc b/cc/resources/picture_layer_tiling.cc
index 171a8cb15242a259dc8e6e8cadcd0e5e1bbd83ba..4f1c8e6593151d09f65d0ef6b953b3ea2af9203a 100644
--- a/cc/resources/picture_layer_tiling.cc
+++ b/cc/resources/picture_layer_tiling.cc
@@ -852,6 +852,13 @@ void PictureLayerTiling::UpdateRequiredStateForTile(Tile* tile,
   tile->set_is_occluded(tree, false);
 }
 
+void PictureLayerTiling::VerifyAllTilesHaveCurrentRasterSource() const {
+#if DCHECK_IS_ON()
+  for (const auto& tile_pair : tiles_)
+    DCHECK_EQ(raster_source_.get(), tile_pair.second->raster_source());
+#endif
+}
+
 TilePriority PictureLayerTiling::ComputePriorityForTile(
     const Tile* tile) const {
   // TODO(vmpstr): See if this can be moved to iterators.