Notify GCMAppHandlers when the store is reset, so they clear cached IDs

chrome/browser/push_messaging/push_messaging_app_identifier.cc

Index: chrome/browser/push_messaging/push_messaging_app_identifier.cc
diff --git a/chrome/browser/push_messaging/push_messaging_app_identifier.cc b/chrome/browser/push_messaging/push_messaging_app_identifier.cc
index 75bed68045171e58f2350bfebeacbcf660f1c85a..fc2f52a0b67c7e18970365411e5bfa1d14be4990 100644
--- a/chrome/browser/push_messaging/push_messaging_app_identifier.cc
+++ b/chrome/browser/push_messaging/push_messaging_app_identifier.cc
@@ -160,6 +160,14 @@ std::vector<PushMessagingAppIdentifier> PushMessagingAppIdentifier::GetAll(
 }
 
 // static
+void PushMessagingAppIdentifier::DeleteAllFromPrefs(Profile* profile) {
+  DictionaryPrefUpdate update(profile->GetPrefs(),
+                              prefs::kPushMessagingAppIdentifierMap);
+  base::DictionaryValue* map = update.Get();
+  map->Clear();
+}
+
+// static
 size_t PushMessagingAppIdentifier::GetCount(Profile* profile) {
   return profile->GetPrefs()
       ->GetDictionary(prefs::kPushMessagingAppIdentifierMap)