Fix a race condition in preference metric reporting.

base/prefs/json_pref_store.h

Index: base/prefs/json_pref_store.h
diff --git a/base/prefs/json_pref_store.h b/base/prefs/json_pref_store.h
index 9e6c1821834e712496f6cf481fc501a56bbfab30..95ecfbb56255577bba1856c9937f734f91cecb3d 100644
--- a/base/prefs/json_pref_store.h
+++ b/base/prefs/json_pref_store.h
@@ -13,6 +13,7 @@
 #include "base/files/file_path.h"
 #include "base/files/important_file_writer.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/memory/scoped_vector.h"
 #include "base/message_loop/message_loop_proxy.h"
 #include "base/observer_list.h"
 #include "base/prefs/base_prefs_export.h"
@@ -51,6 +52,10 @@ class BASE_PREFS_EXPORT JsonPrefStore
   virtual bool HasObservers() const OVERRIDE;
   virtual bool IsInitializationComplete() const OVERRIDE;
 
+  // Adds an observer that will be automatically deregistered and destroyed by
+  // ~JsonPrefStore().
+  void AddOwnedObserver(scoped_ptr<PrefStore::Observer> observer);

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

#include base/prefs/pref_store.h

for PrefStore::Observer

[robertshield, 2013/11/28 02:54:26]

AddObserver takes a raw pointer, any reason not to make this do so as well?

[erikwright (departed), 2013/11/28 17:48:07]

Because there is a transfer of ownership.

+
   // PersistentPrefStore overrides:
   virtual bool GetMutableValue(const std::string& key,
                                base::Value** result) OVERRIDE;
@@ -89,6 +94,7 @@ class BASE_PREFS_EXPORT JsonPrefStore
   base::ImportantFileWriter writer_;
 
   ObserverList<PrefStore::Observer, true> observers_;
+  ScopedVector<PrefStore::Observer> owned_observers_;
 
   scoped_ptr<ReadErrorDelegate> error_delegate_;