Add onChanged events to the extension settings API, both from sync and between

chrome/browser/extensions/extension_settings_storage_quota_enforcer.cc

 // Copyright (c) 2011 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/extensions/extension_settings_storage_quota_enforcer.h"
 
 #include "base/bind.h"
 #include "base/json/json_writer.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/message_loop.h"
@@ skipping 72 matching lines @@
       max_keys_(max_keys),
       delegate_(delegate),
       used_total_(0) {
   Result maybe_initial_settings = delegate->Get();
   if (maybe_initial_settings.HasError()) {
     LOG(WARNING) << "Failed to get initial settings for quota: " <<
         maybe_initial_settings.GetError();
     return;
   }
 
-  DictionaryValue* initial_settings = maybe_initial_settings.GetSettings();
+  const DictionaryValue* initial_settings =
+      maybe_initial_settings.GetSettings();
   for (DictionaryValue::key_iterator it = initial_settings->begin_keys();
       it != initial_settings->end_keys(); ++it) {
     Value *value;
     initial_settings->GetWithoutPathExpansion(*it, &value);
     Allocate(*it, *value, &used_total_, &used_per_setting_);
   }
 }
 
 ExtensionSettingsStorageQuotaEnforcer::~ExtensionSettingsStorageQuotaEnforcer(
     ) {}
@@ skipping 99 matching lines @@
   Result result = delegate_->Clear();
   if (result.HasError()) {
     return result;
   }
 
   while (!used_per_setting_.empty()) {
     Free(&used_total_, &used_per_setting_, used_per_setting_.begin()->first);
   }
   return result;
 }