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

cc/base/invalidation_region.cc

 // 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.
 
 #include "cc/base/invalidation_region.h"
 
 #include "base/metrics/histogram.h"
 
 namespace {
 
 const int kMaxInvalidationRectCount = 256;
 
 }  // namespace
 
 namespace cc {
 
 InvalidationRegion::InvalidationRegion() {}
 
 InvalidationRegion::~InvalidationRegion() {}
 
 void InvalidationRegion::Swap(Region* region) {
   region_.Swap(region);
 }
 
 void InvalidationRegion::Clear() {
   region_.Clear();
 }
 
-void InvalidationRegion::Union(gfx::Rect rect) {
+void InvalidationRegion::Union(const gfx::Rect& rect) {
   region_.Union(rect);
   SimplifyIfNeeded();
 }
 
 void InvalidationRegion::SimplifyIfNeeded() {
   if (region_.GetRegionComplexity() > kMaxInvalidationRectCount)
     region_ = region_.bounds();
 }
 
 }  // namespace cc