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

content/browser/renderer_host/input/touch_emulator_unittest.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 "content/browser/renderer_host/input/touch_emulator.h"
 
 #include <stddef.h>
 
 #include <memory>
 #include <vector>
@@ skipping 201 matching lines @@
   bool SendTouchEvent(WebInputEvent::Type type, WebTouchPoint::State state,
       int x, int y, bool ack) {
     WebTouchEvent event = MakeTouchEvent(type, state, x, y);
     if (emulator()->HandleTouchEvent(event)) {
       // Touch event is not forwarded.
       return false;
     }
 
     if (ack) {
       // Can't send ack if there are some pending acks.
-      DCHECK(!touch_events_to_ack_.size());
+      DCHECK(touch_events_to_ack_.empty());
 
       // Touch event is forwarded, ack should not be handled by emulator.
       EXPECT_FALSE(emulator()->HandleTouchEventAck(
           event, INPUT_EVENT_ACK_STATE_CONSUMED));
     } else {
       touch_events_to_ack_.push_back(event);
     }
     return true;
   }
 
@@ skipping 330 matching lines @@
   emulator()->Disable();
   EXPECT_EQ("TouchStart TouchCancel", ExpectedEvents());
   emulator()->CancelTouch();
 }
 
 TEST_F(TouchEmulatorTest, ConstructorWithHighDeviceScaleDoesNotCrash) {
   TouchEmulator(this, 4.0f);
 }
 
 }  // namespace content