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

ui/app_list/cocoa/app_list_view_controller.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/app_list_view_controller.h"
 
 #include "base/mac/foundation_util.h"
-#include "base/string_util.h"
+#include "base/strings/string_util.h"
 #include "skia/ext/skia_utils_mac.h"
 #include "ui/app_list/app_list_constants.h"
 #include "ui/app_list/app_list_model.h"
 #include "ui/app_list/app_list_view_delegate.h"
 #import "ui/app_list/cocoa/app_list_pager_view.h"
 #import "ui/app_list/cocoa/apps_grid_controller.h"
 #import "ui/base/cocoa/flipped_view.h"
 #include "ui/app_list/search_box_model.h"
 #include "ui/gfx/scoped_ns_graphics_context_save_gstate_mac.h"
 
@@ skipping 252 matching lines @@
 }
 
 - (void)openResult:(app_list::SearchResult*)result {
   if (delegate_)
     delegate_->OpenSearchResult(result, 0 /* event flags */);
 
   [appsSearchBoxController_ clearSearch];
 }
 
 @end