Do not typedef ExtensionId/ID, since it's already available in extension_id.h

extensions/browser/api/alarms/alarm_manager.h

 // Copyright (c) 2012 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 EXTENSIONS_BROWSER_API_ALARMS_ALARM_MANAGER_H_
 #define EXTENSIONS_BROWSER_API_ALARMS_ALARM_MANAGER_H_
 
 #include <map>
 #include <queue>
 #include <string>
 #include <vector>
 
 #include "base/callback.h"
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/scoped_observer.h"
 #include "base/timer/timer.h"
 #include "extensions/browser/browser_context_keyed_api_factory.h"
 #include "extensions/browser/extension_registry_observer.h"
 #include "extensions/common/api/alarms.h"
+#include "extensions/common/extension_id.h"
 
 namespace base {
 class Clock;
 }  // namespace base
 
 namespace content {
 class BrowserContext;
 }  // namespace content
 
 namespace extensions {
@@ skipping 96 matching lines @@
   FRIEND_TEST_ALL_PREFIXES(ExtensionAlarmsSchedulingTest, TimerRunning);
   FRIEND_TEST_ALL_PREFIXES(ExtensionAlarmsSchedulingTest, MinimumGranularity);
   FRIEND_TEST_ALL_PREFIXES(ExtensionAlarmsSchedulingTest,
                            DifferentMinimumGranularities);
   FRIEND_TEST_ALL_PREFIXES(ExtensionAlarmsSchedulingTest,
                            RepeatingAlarmsScheduledPredictably);
   FRIEND_TEST_ALL_PREFIXES(ExtensionAlarmsSchedulingTest,
                            PollFrequencyFromStoredAlarm);
   friend class BrowserContextKeyedAPIFactory<AlarmManager>;
 
-  typedef std::string ExtensionId;
   typedef std::map<ExtensionId, AlarmList> AlarmMap;
 
   typedef base::Callback<void(const std::string&)> ReadyAction;
   typedef std::queue<ReadyAction> ReadyQueue;
   typedef std::map<ExtensionId, ReadyQueue> ReadyMap;
 
   // Iterator used to identify a particular alarm within the Map/List pair.
   // "Not found" is represented by <alarms_.end(), invalid_iterator>.
   typedef std::pair<AlarmMap::iterator, AlarmList::iterator> AlarmIterator;
 
@@ skipping 94 matching lines @@
 
   // Next poll's time.
   base::Time next_poll_time_;
 
   DISALLOW_COPY_AND_ASSIGN(AlarmManager);
 };
 
 }  //  namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_API_ALARMS_ALARM_MANAGER_H_