Increase warning level to 4 on Visual Studio

views/view_win.cc

 // Copyright (c) 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 "views/view.h"
 
 #include <atlcomcli.h>
 //  Necessary to define oleacc GUID's used in window_win.cc.
 #include <initguid.h>
 #include <oleacc.h>
 
 #include "base/string_util.h"
 #include "ui/base/dragdrop/drag_drop_types.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/path.h"
 #include "views/accessibility/native_view_accessibility_win.h"
 #include "views/border.h"
 #include "views/views_delegate.h"
 #include "views/widget/root_view.h"
 #include "views/widget/widget.h"
 #include "views/widget/widget_win.h"
 
 namespace views {
 
 NativeViewAccessibilityWin* View::GetNativeViewAccessibilityWin() {
   if (!native_view_accessibility_win_.get())
-    native_view_accessibility_win_.swap(
-        NativeViewAccessibilityWin::Create(this));
+    native_view_accessibility_win_ =
+        NativeViewAccessibilityWin::Create(this);
   return native_view_accessibility_win_.get();
 }
 
 int View::GetHorizontalDragThreshold() {
   static int threshold = -1;
   if (threshold == -1)
     threshold = GetSystemMetrics(SM_CXDRAG) / 2;
   return threshold;
 }
 
 int View::GetVerticalDragThreshold() {
   static int threshold = -1;
   if (threshold == -1)
     threshold = GetSystemMetrics(SM_CYDRAG) / 2;
   return threshold;
 }
 
 }  // namespace views