[CleanUp] Use base::STLSetDifference in place of std::set_difference

ui/base/test/ui_cocoa_test_helper.mm

 // Copyright (c) 2012 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.
 
 #import "ui/base/test/ui_cocoa_test_helper.h"
 
 #include "base/debug/debugger.h"
 #include "base/logging.h"
+#include "base/stl_util.h"
 #include "base/test/test_timeouts.h"
 
 @implementation CocoaTestHelperWindow
 
 - (id)initWithContentRect:(NSRect)contentRect {
   return [self initWithContentRect:contentRect
                          styleMask:NSBorderlessWindowMask
                            backing:NSBackingStoreBuffered
                              defer:NO];
 }
@@ skipping 153 matching lines @@
   base::mac::ScopedNSAutoreleasePool pool;
   NSArray *appWindows = [NSApp windows];
   for (NSWindow *window in appWindows) {
     windows.insert(window);
   }
   return windows;
 }
 
 std::set<NSWindow*> CocoaTest::WindowsLeft() {
   const std::set<NSWindow*> windows(ApplicationWindows());
-  std::set<NSWindow*> windows_left;
-  std::set_difference(windows.begin(), windows.end(),
-                      initial_windows_.begin(), initial_windows_.end(),
-                      std::inserter(windows_left, windows_left.begin()));
+  std::set<NSWindow*> windows_left =
+      base::STLSetDifference<std::set<NSWindow*> >(windows, initial_windows_);
   return windows_left;
 }
 
 CocoaTestHelperWindow* CocoaTest::test_window() {
   if (!test_window_) {
     test_window_ = [[CocoaTestHelperWindow alloc] init];
     if (base::debug::BeingDebugged()) {
       [test_window_ orderFront:nil];
     } else {
       [test_window_ orderBack:nil];
     }
   }
   return test_window_;
 }
 
 }  // namespace ui