Use a direct include of strings headers, delete some strings forwarding headers.

ui/app_list/cocoa/apps_search_results_controller_unittest.mm

 // Copyright 2013 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/app_list/cocoa/apps_search_results_controller.h"
 
 #include "base/memory/scoped_nsobject.h"
-#include "base/stringprintf.h"
+#include "base/strings/stringprintf.h"
 #include "base/strings/sys_string_conversions.h"
 #include "base/strings/utf_string_conversions.h"
 #import "testing/gtest_mac.h"
 #include "ui/app_list/search_result.h"
 #include "ui/app_list/test/app_list_test_model.h"
 #import "ui/base/test/ui_cocoa_test_helper.h"
 #include "ui/gfx/image/image_skia_util_mac.h"
 
 @interface TestAppsSearchResultsDelegate : NSObject<AppsSearchResultsDelegate> {
  @private
@@ skipping 200 matching lines @@
   // Test activating items.
   EXPECT_TRUE(SimulateKeyAction(@selector(insertNewline:)));
   EXPECT_EQ(ModelResultAt(0), [delegate_ lastOpenedResult]);
   EXPECT_TRUE(SimulateKeyAction(@selector(moveDown:)));
   EXPECT_TRUE(SimulateKeyAction(@selector(insertNewline:)));
   EXPECT_EQ(ModelResultAt(1), [delegate_ lastOpenedResult]);
 }
 
 }  // namespace test
 }  // namespace app_list