Prioritize tiles near the viewport in out-of-viewport layers

cc/resources/picture_layer_tiling.h

Index: cc/resources/picture_layer_tiling.h
diff --git a/cc/resources/picture_layer_tiling.h b/cc/resources/picture_layer_tiling.h
index 67e757aa257c5496bd793df529b534818b41e4a3..bc89dfdffd27d12ff2eb13f171516ae850472c62 100644
--- a/cc/resources/picture_layer_tiling.h
+++ b/cc/resources/picture_layer_tiling.h
@@ -76,6 +76,12 @@ class CC_EXPORT PictureLayerTiling {
       int64 target_area,
       gfx::Rect bounding_rect);
 
+  static gfx::Rect ExpandRectBySizeBoundedBy(
+      gfx::Rect starting_rect,
+      int horizontal_expansion,
+      int vertical_expansion,
+      gfx::Rect bounding_rect);
+
   // Iterate over all tiles to fill content_rect.  Even if tiles are invalid
   // (i.e. no valid resource) this tiling should still iterate over them.
   // The union of all geometry_rect calls for each element iterated over should