Use container::back() and container::pop_back().

cc/trees/single_thread_proxy.cc

 // Copyright 2011 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/trees/single_thread_proxy.h"
 
 #include "base/auto_reset.h"
 #include "base/memory/ptr_util.h"
 #include "base/profiler/scoped_tracker.h"
 #include "base/trace_event/trace_event.h"
@@ skipping 240 matching lines @@
     tracked_objects::ScopedTracker tracking_profile7(
         FROM_HERE_WITH_EXPLICIT_FUNCTION(
             "461509 SingleThreadProxy::DoCommit7"));
     layer_tree_host_->FinishCommitOnImplThread(layer_tree_host_impl_.get());
 
 #if DCHECK_IS_ON()
     // In the single-threaded case, the scale and scroll deltas should never be
     // touched on the impl layer tree.
     std::unique_ptr<ScrollAndScaleSet> scroll_info =
         layer_tree_host_impl_->ProcessScrollDeltas();
-    DCHECK(!scroll_info->scrolls.size());
+    DCHECK(scroll_info->scrolls.empty());
     DCHECK_EQ(1.f, scroll_info->page_scale_delta);
 #endif
 
     if (scheduler_on_impl_thread_)
       scheduler_on_impl_thread_->DidCommit();
 
     layer_tree_host_impl_->CommitComplete();
 
     // TODO(robliao): Remove ScopedTracker below once https://crbug.com/461509
     // is fixed.
@@ skipping 613 matching lines @@
 void SingleThreadProxy::DidFinishImplFrame() {
   layer_tree_host_impl_->DidFinishImplFrame();
 #if DCHECK_IS_ON()
   DCHECK(inside_impl_frame_)
       << "DidFinishImplFrame called while not inside an impl frame!";
   inside_impl_frame_ = false;
 #endif
 }
 
 }  // namespace cc