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

cc/layers/picture_image_layer.cc

 // Copyright 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/layers/picture_image_layer.h"
 
 #include "cc/layers/picture_image_layer_impl.h"
 #include "third_party/skia/include/core/SkCanvas.h"
 
 namespace cc {
@@ skipping 23 matching lines @@
   // affect the actual contents of the image (e.g. a CSS animation).
   // With this check in place we avoid unecessary texture uploads.
   if (bitmap.pixelRef() && bitmap.pixelRef() == bitmap_.pixelRef())
     return;
 
   bitmap_ = bitmap;
   SetNeedsDisplay();
 }
 
 void PictureImageLayer::PaintContents(SkCanvas* canvas,
-                                      gfx::Rect clip,
+                                      const gfx::Rect& clip,
                                       gfx::RectF* opaque) {
   if (!bitmap_.width() || !bitmap_.height())
     return;
 
   SkScalar content_to_layer_scale_x =
       SkFloatToScalar(static_cast<float>(bounds().width()) / bitmap_.width());
   SkScalar content_to_layer_scale_y =
       SkFloatToScalar(static_cast<float>(bounds().height()) / bitmap_.height());
   canvas->scale(content_to_layer_scale_x, content_to_layer_scale_y);
 
   canvas->drawBitmap(bitmap_, 0, 0);
 }
 
 }  // namespace cc