cc: Give non-drawing layers that are rasterized a lower priority.

cc/tiles/picture_layer_tiling.h

Index: cc/tiles/picture_layer_tiling.h
diff --git a/cc/tiles/picture_layer_tiling.h b/cc/tiles/picture_layer_tiling.h
index d49d22ed23fa1e0d4a2c114d635617e3a940e6d5..d9c33a0418a7199e02150fe771eda13909420e3d 100644
--- a/cc/tiles/picture_layer_tiling.h
+++ b/cc/tiles/picture_layer_tiling.h
@@ -126,6 +126,9 @@ class CC_EXPORT PictureLayerTiling {
   void set_can_require_tiles_for_activation(bool can_require_tiles) {
     can_require_tiles_for_activation_ = can_require_tiles;
   }
+  bool can_require_tiles_for_activation() const {
+    return can_require_tiles_for_activation_;
+  }
 
   const scoped_refptr<RasterSource>& raster_source() const {
     return raster_source_;