Disable ExtensionPrefStore for local-state pref store

chrome/browser/extensions/extension_pref_store.h

Index: chrome/browser/extensions/extension_pref_store.h
diff --git a/chrome/browser/extensions/extension_pref_store.h b/chrome/browser/extensions/extension_pref_store.h
index 67c7335c05af5922c705254dd628bee72e0011e5..5928445f8fda43fe4ff592d8a4f0b26243f6d87b 100644
--- a/chrome/browser/extensions/extension_pref_store.h
+++ b/chrome/browser/extensions/extension_pref_store.h
@@ -30,15 +30,6 @@ class Value;
 // proxy settings. A stack of relevant extensions is stored in order of
 // their addition to this PrefStore. For each preference, the last-added
 // enabled extension that tries to set it overrules any others.
-//
-// TODO(battre): The ExtensionPrefStore has an issue if it serves for storing
-// extension preferences in the local-state (shared among all profiles on a
-// machine). In this context, there is no meaningful definition of a precedence
-// order as the same extensions can be installed in different profiles.
-// One instance would override the preferences of another instance. Also it is
-// unclear how settings should be removed in this case. For this reason we
-// (pamg, battre) decided to not support the ExtensionPrefStore for local-state.
-// This needs to be enforced by the code.
 class ExtensionPrefStore : public PrefStore,
                            public NotificationObserver {
  public:
@@ -52,6 +43,11 @@ class ExtensionPrefStore : public PrefStore,
   typedef std::pair<const Extension*, std::pair<const char*, Value*> >
       ExtensionPrefDetails;
 
+  // The local-state ExtensionPrefStore (shared among all profiles on a
+  // machine), indicated by a NULL |profile|, is prohibited from storing
+  // preferences. Since extensions are installed per profile, allowing them to
+  // control machine-wide settings could lead to unsolvable conflicts, and
+  // should not be necessary anyway.
   ExtensionPrefStore(Profile* profile, PrefNotifier::PrefStoreType type);
   virtual ~ExtensionPrefStore();
 
@@ -76,9 +72,7 @@ class ExtensionPrefStore : public PrefStore,
   // This should only be accessed by subclasses for unit-testing.
   void GetExtensionIDs(std::vector<std::string>* result);
 
-  // Returns the applicable pref service from the profile (if we have one) or
-  // the browser's local state. This should only be accessed or overridden by
-  // subclasses for unit-testing.
+  // For PrefService injection for unit-testing
   virtual PrefService* GetPrefService();
 
   // The following functions delegate to