Fix a race condition in preference metric reporting.

chrome/browser/prefs/pref_change_reporter.h

Index: chrome/browser/prefs/pref_change_reporter.h
diff --git a/chrome/browser/prefs/pref_change_reporter.h b/chrome/browser/prefs/pref_change_reporter.h
new file mode 100644
index 0000000000000000000000000000000000000000..8207a91aece08b586106ceb3105617981031ef76
--- /dev/null
+++ b/chrome/browser/prefs/pref_change_reporter.h
@@ -0,0 +1,20 @@
+// 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.
+
+#ifndef CHROME_BROWSER_PREFS_PREF_CHANGE_REPORTER_H_
+#define CHROME_BROWSER_PREFS_PREF_CHANGE_REPORTER_H_
+
+#include "base/memory/scoped_ptr.h"
+
+class JsonPrefStore;
+class PrefHashStore;
+
+// Enables UMA reporting of tracked preference changes in |pref_store|, using
+// |pref_hash_store|. Must be called before |pref_store| has begun loading.
+// |pref_hash_store| will be destroyed when |pref_store| is destroyed.
+// 
+void ReportPrefStoreChangesToUMA(JsonPrefStore* pref_store,

[gab, 2013/11/27 23:43:27]

Change this name to something more generic as this could be used in the future
to do more than UMA.

+                                 scoped_ptr<PrefHashStore> pref_hash_store);
+
+#endif  // CHROME_BROWSER_PREFS_PREF_CHANGE_REPORTER_H_