Clean up SkFontConfigInterface implementation.

src/ports/SkFontConfigInterface_direct_factory.cpp

 /*
  * Copyright 2009-2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
-/* migrated from chrome/src/skia/ext/SkFontHost_fontconfig_direct.cpp */
+#include "SkFontConfigInterface_direct.h"
+#include "SkOnce.h"
 
-#include "SkFontConfigInterface_direct.h"
-#include "SkMutex.h"
-
-SkFontConfigInterface* SkFontConfigInterface::GetSingletonDirectInterface(SkBaseMutex* mutex) {
-    SkAutoMutexAcquire ac(mutex);
-    static SkFontConfigInterfaceDirect* singleton = nullptr;
-    if (singleton == nullptr) {
-        singleton = new SkFontConfigInterfaceDirect;
-    }
+SkFontConfigInterface* SkFontConfigInterface::GetSingletonDirectInterface() {
+    static SkFontConfigInterface* singleton;
+    static SkOnce once;
+    once([]{ singleton = new SkFontConfigInterfaceDirect(); });
     return singleton;
 }