Add InvalidationStateTracker::Forget() to erase an entry from storage.

sync/notifier/fake_invalidation_state_tracker.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 SYNC_NOTIFIER_FAKE_INVALIDATION_STATE_TRACKER_H_
 #define SYNC_NOTIFIER_FAKE_INVALIDATION_STATE_TRACKER_H_
 
 #include "base/memory/weak_ptr.h"
 #include "sync/notifier/invalidation_state_tracker.h"
 
 namespace syncer {
 
 // InvalidationStateTracker implementation that simply keeps track of
 // the max versions and invalidation state in memory.
 class FakeInvalidationStateTracker
     : public InvalidationStateTracker,
       public base::SupportsWeakPtr<FakeInvalidationStateTracker> {
  public:
   FakeInvalidationStateTracker();
   virtual ~FakeInvalidationStateTracker();
 
+  int64 GetMaxVersion(const invalidation::ObjectId& id) const;
+
   // InvalidationStateTracker implementation.
   virtual InvalidationVersionMap GetAllMaxVersions() const OVERRIDE;
   virtual void SetMaxVersion(const invalidation::ObjectId& id,
                              int64 max_version) OVERRIDE;
-  int64 GetMaxVersion(const invalidation::ObjectId& id) const;
+  virtual void Forget(const ObjectIdSet& ids) OVERRIDE;
   virtual void SetInvalidationState(const std::string& state) OVERRIDE;
   virtual std::string GetInvalidationState() const OVERRIDE;
 
   static const int64 kMinVersion;
 
  private:
   InvalidationVersionMap versions_;
   std::string state_;
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_NOTIFIER_FAKE_INVALIDATION_STATE_TRACKER_H_