Use container::back() and container::pop_back() in ui/

ui/compositor/layer_animator_collection.cc

 // Copyright 2014 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 "ui/compositor/layer_animator_collection.h"
 
 #include <set>
 
 #include "base/time/time.h"
 #include "ui/compositor/compositor.h"
 #include "ui/compositor/layer_animator.h"
 
 namespace ui {
 
 LayerAnimatorCollection::LayerAnimatorCollection(Compositor* compositor)
     : compositor_(compositor), last_tick_time_(base::TimeTicks::Now()) {
 }
 
 LayerAnimatorCollection::~LayerAnimatorCollection() {
   if (compositor_)
     compositor_->RemoveAnimationObserver(this);
 }
 
 void LayerAnimatorCollection::StartAnimator(
     scoped_refptr<LayerAnimator> animator) {
   DCHECK_EQ(0U, animators_.count(animator));
-  if (!animators_.size())
+  if (animators_.empty())
     last_tick_time_ = base::TimeTicks::Now();
   animators_.insert(animator);
   if (animators_.size() == 1U && compositor_)
     compositor_->AddAnimationObserver(this);
 }
 
 void LayerAnimatorCollection::StopAnimator(
     scoped_refptr<LayerAnimator> animator) {
   DCHECK_GT(animators_.count(animator), 0U);
   animators_.erase(animator);
@@ skipping 20 matching lines @@
 }
 
 void LayerAnimatorCollection::OnCompositingShuttingDown(
     Compositor* compositor) {
   DCHECK_EQ(compositor_, compositor);
   compositor_->RemoveAnimationObserver(this);
   compositor_ = nullptr;
 }
 
 }  // namespace ui