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

chrome/browser/spellchecker/spellcheck_service_browsertest.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/spellchecker/spellcheck_service.h"
 
 #include <stddef.h>
 #include <stdint.h>
 #include <string>
 #include <tuple>
 #include <vector>
 
 #include "base/command_line.h"
 #include "base/macros.h"
 #include "base/path_service.h"
 #include "base/run_loop.h"
+#include "base/strings/string_piece.h"
 #include "base/strings/string_split.h"
 #include "base/strings/string_util.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/values.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/spellchecker/spellcheck_factory.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/common/chrome_paths.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/pref_names.h"
@@ skipping 95 matching lines @@
     base::ListValue dictionaries_value;
     dictionaries_value.AppendStrings(
         base::SplitString(multiple_dictionaries, ",", base::TRIM_WHITESPACE,
                           base::SPLIT_WANT_NONEMPTY));
     prefs_->Set(spellcheck::prefs::kSpellCheckDictionaries, dictionaries_value);
   }
 
   std::string GetMultilingualDictionaries() {
     const base::ListValue* list_value =
         prefs_->GetList(spellcheck::prefs::kSpellCheckDictionaries);
-    std::vector<std::string> dictionaries;
+    std::vector<base::StringPiece> dictionaries;
     for (const auto& item_value : *list_value) {
-      std::string dictionary;
+      base::StringPiece dictionary;
       EXPECT_TRUE(item_value->GetAsString(&dictionary));
       dictionaries.push_back(dictionary);
     }
     return base::JoinString(dictionaries, ",");
   }
 
   void SetAcceptLanguages(const std::string& accept_languages) {
     ScopedPreferenceChange scope(&renderer_->sink());
     prefs_->SetString(prefs::kAcceptLanguages, accept_languages);
   }
@@ skipping 247 matching lines @@
   std::string pref;
   ASSERT_TRUE(GetPrefs()
                   ->GetList(spellcheck::prefs::kSpellCheckDictionaries)
                   ->GetString(0, &pref));
   EXPECT_EQ("en-US", pref);
   ASSERT_TRUE(GetPrefs()
                   ->GetList(spellcheck::prefs::kSpellCheckDictionaries)
                   ->GetString(1, &pref));
   EXPECT_EQ("fr", pref);
 }