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

tests/AtomicTest.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
-#include "SkAtomics.h"
+#include "SkThread.h"
 #include "SkThreadUtils.h"
 #include "SkTypes.h"
 #include "Test.h"
 
 struct AddInfo {
     int32_t valueToAdd;
     int timesToAdd;
     unsigned int processorAffinity;
 };
 
@@ skipping 29 matching lines @@
     for (size_t i = 0; i < SK_ARRAY_COUNT(gAdds); i++) {
         threads[i]->join();
         delete threads[i];
     }
     REPORTER_ASSERT(reporter, total == base);
     // Ensure that the returned value from sk_atomic_add is correct.
     int32_t valueToModify = 3;
     const int32_t originalValue = valueToModify;
     REPORTER_ASSERT(reporter, originalValue == sk_atomic_add(&valueToModify, 7));
 }