Revert "Remove SkThread.h from public API."

include/core/SkOnce.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 SkOnce_DEFINED
 #define SkOnce_DEFINED
 
@@ skipping 11 matching lines @@
 //     SkOnce(&once, set_up_my_singleton, &singleton);
 //     SkASSERT(NULL != singleton);
 //     return *singleton;
 // }
 //
 // OnceTest.cpp also should serve as a few other simple examples.
 //
 // You may optionally pass SkOnce a second function to be called at exit for cleanup.
 
 #include "SkDynamicAnnotations.h"
+#include "SkThread.h"
 #include "SkTypes.h"
 
-#include "../../src/core/SkThread.h"
-
 #define SK_ONCE_INIT { false, { 0, SkDEBUGCODE(0) } }
 #define SK_DECLARE_STATIC_ONCE(name) static SkOnceFlag name = SK_ONCE_INIT
 
 struct SkOnceFlag;  // If manually created, initialize with SkOnceFlag once = SK_ONCE_INIT
 
 template <typename Func, typename Arg>
 inline void SkOnce(SkOnceFlag* once, Func f, Arg arg, void(*atExit)() = NULL);
 
 // If you've already got a lock and a flag to use, this variant lets you avoid an extra SkOnceFlag.
 template <typename Lock, typename Func, typename Arg>
@@ skipping 123 matching lines @@
 }
 
 template <typename Func, typename Arg>
 inline void SkOnce(SkOnceFlag* once, Func f, Arg arg, void(*atExit)()) {
     return SkOnce(&once->done, &once->lock, f, arg, atExit);
 }
 
 #undef SK_ANNOTATE_BENIGN_RACE
 
 #endif  // SkOnce_DEFINED