[#2] Pass gfx structs by const ref (gfx::Rect, gfx::RectF)

cc/output/copy_output_request.h

Index: cc/output/copy_output_request.h
diff --git a/cc/output/copy_output_request.h b/cc/output/copy_output_request.h
index 4b74b419fcace7651691baa3616bfb4921993324..6d8870d88f4905118f6698a6d9fbe26afde199b6 100644
--- a/cc/output/copy_output_request.h
+++ b/cc/output/copy_output_request.h
@@ -46,7 +46,7 @@ class CC_EXPORT CopyOutputRequest {
   // By default copy requests copy the entire layer's subtree output. If an
   // area is given, then the intersection of this rect (in layer space) with
   // the layer's subtree output will be returned.
-  void set_area(gfx::Rect area) {
+  void set_area(const gfx::Rect& area) {
     has_area_ = true;
     area_ = area;
   }