cc: Eliminate refcount churn in prioritized tile's raster source.

cc/tiles/prioritized_tile.cc

Index: cc/tiles/prioritized_tile.cc
diff --git a/cc/tiles/prioritized_tile.cc b/cc/tiles/prioritized_tile.cc
index 5b5c05a7e3a877f6599823fa48f7dbeac8214da2..526138bd8d1d37ee839204f8d81975e202768b36 100644
--- a/cc/tiles/prioritized_tile.cc
+++ b/cc/tiles/prioritized_tile.cc
@@ -9,25 +9,19 @@
 
 namespace cc {
 
-PrioritizedTile::PrioritizedTile() : tile_(nullptr), is_occluded_(false) {}
+PrioritizedTile::PrioritizedTile() = default;
 
 PrioritizedTile::PrioritizedTile(Tile* tile,
-                                 scoped_refptr<RasterSource> raster_source,
+                                 const PictureLayerTiling* source_tiling,
                                  const TilePriority priority,
                                  bool is_occluded)
     : tile_(tile),
-      raster_source_(std::move(raster_source)),
+      source_tiling_(source_tiling),
       priority_(priority),
       is_occluded_(is_occluded) {}
 
-PrioritizedTile::PrioritizedTile(const PrioritizedTile& other) = default;
-PrioritizedTile::PrioritizedTile(PrioritizedTile&& other) = default;
 PrioritizedTile::~PrioritizedTile() = default;
 
-PrioritizedTile& PrioritizedTile::operator=(const PrioritizedTile& other) =
-    default;
-PrioritizedTile& PrioritizedTile::operator=(PrioritizedTile&& other) = default;
-
 void PrioritizedTile::AsValueInto(base::trace_event::TracedValue* value) const {
   tile_->AsValueInto(value);