Fix race condition in parallel font initialization.

include/ports/SkFontConfigInterface.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkFontConfigInterface_DEFINED
 #define SkFontConfigInterface_DEFINED
 
 #include "SkDataTable.h"
 #include "SkFontStyle.h"
 #include "SkRefCnt.h"
 #include "SkTArray.h"
 #include "SkTypeface.h"
 
+struct SkBaseMutex;
+
 /**
  *  \class SkFontConfigInterface
  *
  *  Provides SkFontHost clients with access to fontconfig services. They will
  *  access the global instance found in RefGlobal().
  */
 class SK_API SkFontConfigInterface : public SkRefCnt {
 public:
     SK_DECLARE_INST_COUNT(SkFontConfigInterface)
 
@@ skipping 61 matching lines @@
     /**
      *  Given a FontRef, open a stream to access its data, or return null
      *  if the FontRef's data is not available. The caller is responsible for
      *  calling stream->unref() when it is done accessing the data.
      */
     virtual SkStream* openStream(const FontIdentity&) = 0;
 
     /**
      *  Return a singleton instance of a direct subclass that calls into
      *  libfontconfig. This does not affect the refcnt of the returned instance.
+     *  The mutex may be used to guarantee the singleton is only constructed once.
      */
-    static SkFontConfigInterface* GetSingletonDirectInterface();
+    static SkFontConfigInterface* GetSingletonDirectInterface
+        (SkBaseMutex* mutex = NULL);
 
     // New APIS, which have default impls for now (which do nothing)
 
     virtual SkDataTable* getFamilyNames() { return SkDataTable::NewEmpty(); }
     virtual bool matchFamilySet(const char inFamilyName[],
                                 SkString* outFamilyName,
                                 SkTArray<FontIdentity>*) {
         return false;
     }
     typedef SkRefCnt INHERITED;
 };
 
 #endif