Revert of Remove SkThread.h, include SkMutex.h or SkAtomics.h as appropriate.

include/core/SkWeakRefCnt.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 SkWeakRefCnt_DEFINED
 #define SkWeakRefCnt_DEFINED
 
 #include "SkRefCnt.h"
-#include "SkAtomics.h"
+#include "SkThread.h"
 
 /** \class SkWeakRefCnt
 
     SkWeakRefCnt is the base class for objects that may be shared by multiple
     objects. When an existing strong owner wants to share a reference, it calls
     ref(). When a strong owner wants to release its reference, it calls
     unref(). When the shared object's strong reference count goes to zero as
     the result of an unref() call, its (virtual) weak_dispose method is called.
     It is an error for the destructor to be called explicitly (or via the
     object going out of scope on the stack or calling delete) if
@@ skipping 127 matching lines @@
         weak_unref();
     }
 
     /* Invariant: fWeakCnt = #weak + (fRefCnt > 0 ? 1 : 0) */
     mutable int32_t fWeakCnt;
 
     typedef SkRefCnt INHERITED;
 };
 
 #endif