Use a direct include of strings headers in extensions/, google_apis/, gpu/.

google_apis/gaia/oauth2_mint_token_flow.h

 // 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.
 
 #ifndef GOOGLE_APIS_GAIA_OAUTH2_MINT_TOKEN_FLOW_H_
 #define GOOGLE_APIS_GAIA_OAUTH2_MINT_TOKEN_FLOW_H_
 
 #include <string>
 #include <vector>
 
 #include "base/memory/weak_ptr.h"
-#include "base/string16.h"
+#include "base/strings/string16.h"
 #include "google_apis/gaia/oauth2_api_call_flow.h"
 
 class GoogleServiceAuthError;
 class OAuth2MintTokenFlowTest;
 
 namespace base {
 class DictionaryValue;
 }
 
 namespace content {
@@ skipping 115 matching lines @@
       int* time_to_live);
 
   Delegate* delegate_;
   Parameters parameters_;
   base::WeakPtrFactory<OAuth2MintTokenFlow> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(OAuth2MintTokenFlow);
 };
 
 #endif  // GOOGLE_APIS_GAIA_OAUTH2_MINT_TOKEN_FLOW_H_