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

cc/base/invalidation_region.h

 // Copyright 2013 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.
 
 #ifndef CC_BASE_INVALIDATION_REGION_H_
 #define CC_BASE_INVALIDATION_REGION_H_
 
 #include "cc/base/cc_export.h"
 #include "cc/base/region.h"
 #include "ui/gfx/rect.h"
 
 namespace cc {
 
 // This class behaves similarly to Region, but it may have false positives. That
 // is, InvalidationRegion can be simplified to encompass a larger area than the
 // collection of rects unioned.
 class CC_EXPORT InvalidationRegion {
  public:
   InvalidationRegion();
   ~InvalidationRegion();
 
   void Swap(Region* region);
   void Clear();
-  void Union(gfx::Rect rect);
+  void Union(const gfx::Rect& rect);
   bool IsEmpty() const { return region_.IsEmpty(); }
 
  private:
   void SimplifyIfNeeded();
 
   Region region_;
 };
 
 }  // namespace cc
 
 #endif  // CC_BASE_INVALIDATION_REGION_H_