Fix race between ~SkThreadPool and SkThreadPool::Loop on fDone.

include/utils/SkThreadPool.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkThreadPool_DEFINED
 #define SkThreadPool_DEFINED
 
@@ skipping 25 matching lines @@
         // Unowned pointer.
         SkRunnable* fRunnable;
 
     private:
         SK_DECLARE_INTERNAL_LLIST_INTERFACE(LinkedRunnable);
     };
 
     SkTInternalLList<LinkedRunnable>    fQueue;
     SkCondVar                           fReady;
     SkTDArray<SkThread*>                fThreads;
-    bool                            fDone;
+    bool                                fDone;
 
     static void Loop(void*);  // Static because we pass in this.
 };
 
 #endif