cc: Use multiple PrepareTiles approaches

cc/tiles/picture_layer_tiling.cc

Index: cc/tiles/picture_layer_tiling.cc
diff --git a/cc/tiles/picture_layer_tiling.cc b/cc/tiles/picture_layer_tiling.cc
index 03bf211659a017c08cf3c8193b007b8992f6f8fd..194c0cc134867fcfd97004312fffdcea243cb8de 100644
--- a/cc/tiles/picture_layer_tiling.cc
+++ b/cc/tiles/picture_layer_tiling.cc
@@ -813,6 +813,14 @@ bool PictureLayerTiling::IsTileRequiredForDraw(const Tile* tile) const {
   return true;
 }
 
+bool PictureLayerTiling::RasterSourceCoversCurrentVisibleTiles() const {
+  gfx::Rect visible_rect_expanded_to_tile_bounds =
+      tiling_data_.ExpandRectToTileBounds(current_visible_rect_);
+
+  return raster_source_->CoversRect(visible_rect_expanded_to_tile_bounds,
+                                    contents_scale_);
+}
+
 void PictureLayerTiling::UpdateRequiredStatesOnTile(Tile* tile) const {
   DCHECK(tile);
   tile->set_required_for_activation(IsTileRequiredForActivation(tile));