cleanup: pass string as const reference from c/b/extension/api

chrome/browser/extensions/api/spellcheck/spellcheck_api.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 "chrome/browser/extensions/api/spellcheck/spellcheck_api.h"
 
 #include "base/lazy_instance.h"
 #include "chrome/browser/spellchecker/spellcheck_factory.h"
 #include "chrome/browser/spellchecker/spellcheck_service.h"
 #include "chrome/common/extensions/api/spellcheck/spellcheck_handler.h"
 #include "extensions/browser/extension_registry.h"
 #include "extensions/common/manifest_constants.h"
 
 namespace extensions {
 
 namespace errors = manifest_errors;
 
 namespace {
 
 SpellcheckDictionaryInfo* GetSpellcheckDictionaryInfo(
     const Extension* extension) {
   SpellcheckDictionaryInfo *spellcheck_info =
       static_cast<SpellcheckDictionaryInfo*>(
           extension->GetManifestData(manifest_keys::kSpellcheck));
   return spellcheck_info;
 }
 
-SpellcheckService::DictionaryFormat GetDictionaryFormat(std::string format) {
+SpellcheckService::DictionaryFormat GetDictionaryFormat(
+    const std::string& format) {
   if (format == "hunspell") {
     return SpellcheckService::DICT_HUNSPELL;
   } else if (format == "text") {
     return SpellcheckService::DICT_TEXT;
   } else {
     return SpellcheckService::DICT_UNKNOWN;
   }
 }
 
 }  // namespace
@@ skipping 44 matching lines @@
   }
 }
 
 template <>
 void
 BrowserContextKeyedAPIFactory<SpellcheckAPI>::DeclareFactoryDependencies() {
   DependsOn(SpellcheckServiceFactory::GetInstance());
 }
 
 }  // namespace extensions