Use a direct include of strings headers in chrome/browser/r*-s*/.

chrome/browser/status_icons/status_tray_unittest.cc

 // 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.
 
 #include "base/compiler_specific.h"
-#include "base/string_util.h"
+#include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "chrome/browser/status_icons/status_icon.h"
 #include "chrome/browser/status_icons/status_tray.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 using testing::Return;
 
 class MockStatusIcon : public StatusIcon {
   virtual void SetImage(const gfx::ImageSkia& image) OVERRIDE {}
@@ skipping 22 matching lines @@
 // Make sure that removing an icon removes it from the list.
 TEST(StatusTrayTest, CreateRemove) {
   TestStatusTray tray;
   EXPECT_CALL(tray,
       CreatePlatformStatusIcon()).WillOnce(Return(new MockStatusIcon()));
   StatusIcon* icon = tray.CreateStatusIcon();
   EXPECT_EQ(1U, tray.status_icons_.size());
   tray.RemoveStatusIcon(icon);
   EXPECT_EQ(0U, tray.status_icons_.size());
 }