Add utf_string_conversions to base namespace.

chrome/browser/extensions/external_pref_loader.cc

Index: chrome/browser/extensions/external_pref_loader.cc
diff --git a/chrome/browser/extensions/external_pref_loader.cc b/chrome/browser/extensions/external_pref_loader.cc
index b0c89d20d78d6516eeb52f664fd053f9ea054ae9..f03022334ee77e9b6dbc4cab2432bc3edc30c554 100644
--- a/chrome/browser/extensions/external_pref_loader.cc
+++ b/chrome/browser/extensions/external_pref_loader.cc
@@ -40,7 +40,7 @@ std::set<base::FilePath> GetPrefsCandidateFilesFromFolder(
       false,  // Recursive.
       file_util::FileEnumerator::FILES);
 #if defined(OS_WIN)
-  base::FilePath::StringType extension = UTF8ToWide(std::string(".json"));
+  base::FilePath::StringType extension = base::UTF8ToWide(std::string(".json"));
 #elif defined(OS_POSIX)
   base::FilePath::StringType extension(".json");
 #endif
@@ -210,7 +210,7 @@ void ExternalPrefLoader::ReadStandaloneExtensionPrefFiles(
 
     std::string id =
 #if defined(OS_WIN)
-        WideToASCII(
+        base::WideToASCII(
             extension_candidate_path.RemoveExtension().BaseName().value());
 #elif defined(OS_POSIX)
         extension_candidate_path.RemoveExtension().BaseName().value().c_str();