Avoid setIndexedDBClientCreateFunction() write race.

third_party/WebKit/Source/modules/indexeddb/IndexedDBClient.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "modules/indexeddb/IndexedDBClient.h"
+#include "wtf/Atomics.h"
 
 namespace blink {
 
-static CreateIndexedDBClient* idbClientCreateFunction = nullptr;
+static void* idbClientCreateFunction = nullptr;
 
 void setIndexedDBClientCreateFunction(CreateIndexedDBClient createFunction)
 {
-    idbClientCreateFunction = createFunction;
+#if ENABLE(ASSERT)
+    CreateIndexedDBClient* currentFunction = reinterpret_cast<CreateIndexedDBClient*>(acquireLoad(&idbClientCreateFunction));
+    ASSERT(!currentFunction || currentFunction == createFunction);
+#endif
+    releaseStore(&idbClientCreateFunction, reinterpret_cast<void*>(createFunction));
 }
 
 IndexedDBClient* IndexedDBClient::create()
 {
     ASSERT(idbClientCreateFunction);
     // There's no reason why we need to allocate a new proxy each time, but
     // there's also no strong reason not to.
-    return idbClientCreateFunction();
+    return reinterpret_cast<CreateIndexedDBClient*>(idbClientCreateFunction)();
 }
 
 } // namespace blink