Fix race condition in parallel font initialization.

include/ports/SkFontConfigInterface.h

Index: include/ports/SkFontConfigInterface.h
diff --git a/include/ports/SkFontConfigInterface.h b/include/ports/SkFontConfigInterface.h
index 8c12a5628ad05bf9e2ef625f7f7d53921474de10..c3a2bbc8c890fea96b273a5288e7570635a29b99 100644
--- a/include/ports/SkFontConfigInterface.h
+++ b/include/ports/SkFontConfigInterface.h
@@ -12,6 +12,7 @@
 #include "SkFontStyle.h"
 #include "SkRefCnt.h"
 #include "SkTArray.h"
+#include "SkThread.h"
 #include "SkTypeface.h"
 
 /**
@@ -95,8 +96,9 @@ public:
     /**
      *  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);

[mtklein, 2014/06/26 18:59:07]

Would mildly prefer passing this as a pointer.

[tomhudson, 2014/06/26 21:01:52]

I wish for pointers just to avoid the #include. I'd made it a reference to
guarantee non-NULL, but it looks like SkAutoMutexAcquire has sane NULL-handling,
so...

Done 

[mtklein, 2014/06/26 21:05:31]

Just FYI, you can forward declare types used as references too.

 
     // New APIS, which have default impls for now (which do nothing)