Fix a race condition in preference metric reporting.

chrome/browser/prefs/pref_hash_store.cc

Index: chrome/browser/prefs/pref_hash_store.cc
diff --git a/chrome/browser/prefs/pref_hash_store.cc b/chrome/browser/prefs/pref_hash_store.cc
new file mode 100644
index 0000000000000000000000000000000000000000..32c3abb9c7d8eb60c320cc3406cffd18995b821f
--- /dev/null
+++ b/chrome/browser/prefs/pref_hash_store.cc
@@ -0,0 +1,13 @@
+// Copyright 2013 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 "chrome/browser/prefs/pref_hash_store.h"
+
+#include "chrome/browser/prefs/pref_hash_tracker.h"
+
+//static 
+scoped_ptr<PrefHashTracker> PrefHashStore::CreateTracker(
+    scoped_ptr<PrefHashStore> builder) {
+  return builder->CompleteInitialization();
+}