Change uses of base::JoinString to pass StringPieces where possible.

chrome/browser/extensions/api/identity/gaia_web_auth_flow.cc

 // Copyright (c) 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.
 
 #include "chrome/browser/extensions/api/identity/gaia_web_auth_flow.h"
 
 #include "base/strings/string_number_conversions.h"
+#include "base/strings/string_piece.h"
 #include "base/strings/string_split.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/trace_event/trace_event.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/signin/chrome_signin_client_factory.h"
 #include "chrome/browser/signin/profile_oauth2_token_service_factory.h"
 #include "chrome/browser/signin/signin_manager_factory.h"
 #include "components/signin/core/browser/profile_oauth2_token_service.h"
 #include "components/signin/core/browser/signin_manager.h"
@@ skipping 30 matching lines @@
       "client_id=%s&"
       "scope=%s&"
       "origin=chrome-extension://%s/&"
       "redirect_uri=%s:/%s&"
       "hl=%s";
   // Additional parameters to pass if device_id is enabled.
   const char kOAuth2AuthorizeFormatDeviceIdAddendum[] =
       "&device_id=%s&"
       "device_type=chrome";
 
-  std::vector<std::string> scopes(token_key->scopes.begin(),
-                                  token_key->scopes.end());
-  std::vector<std::string> client_id_parts = base::SplitString(
+  std::vector<base::StringPiece> scopes(token_key->scopes.begin(),
+                                        token_key->scopes.end());
+  std::vector<base::StringPiece> client_id_parts = base::SplitStringPiece(
       oauth2_client_id, ".", base::TRIM_WHITESPACE, base::SPLIT_WANT_ALL);
   std::reverse(client_id_parts.begin(), client_id_parts.end());
   redirect_scheme_ = base::JoinString(client_id_parts, ".");
   std::string signin_scoped_device_id;
   // profile_ can be nullptr in unittests.
   SigninClient* signin_client =
       profile_ ? ChromeSigninClientFactory::GetForProfile(profile_) : nullptr;
   if (signin_client)
     signin_scoped_device_id = signin_client->GetSigninScopedDeviceId();
 
@@ skipping 228 matching lines @@
       FROM_HERE,
       base::Bind(&GaiaWebAuthFlow::StartUberTokenFetch,
                  gaia_web_auth_flow_));
 }
 
 void GaiaWebAuthFlow::IOHelper::Cleanup() {
   delete this;
 }
 
 }  // namespace extensions