[Chromoting] Refactor the host policy watcher so that policies can easily be added.

remoting/host/policy_hack/nat_policy.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 REMOTING_HOST_POLICY_HACK_NAT_POLICY_H_
-#define REMOTING_HOST_POLICY_HACK_NAT_POLICY_H_
-
-#include "base/callback.h"
-#include "base/memory/weak_ptr.h"
-
-namespace base {
-class DictionaryValue;
-class SingleThreadTaskRunner;
-class TimeDelta;
-class WaitableEvent;
-}  // namespace base
-
-namespace remoting {
-namespace policy_hack {
-
-// Watches for changes to the managed remote access host NAT policies.
-// If StartWatching() has been called, then before this object can be deleted,
-// StopWatching() have completed (the provided |done| event must be signaled).
-class NatPolicy {
- public:
-  // Called with the current status of whether or not NAT traversal is enabled.
-  typedef base::Callback<void(bool)> NatEnabledCallback;
-
-  explicit NatPolicy(scoped_refptr<base::SingleThreadTaskRunner> task_runner);
-  virtual ~NatPolicy();
-
-  // This guarantees that the |nat_enabled_cb| is called at least once with
-  // the current policy.  After that, |nat_enabled_cb| will be called whenever
-  // a change to the nat policy is detected.
-  virtual void StartWatching(const NatEnabledCallback& nat_enabled_cb);
-
-  // Should be called after StartWatching() before the object is deleted. Calls
-  // just wait for |done| to be signaled before deleting the object.
-  virtual void StopWatching(base::WaitableEvent* done);
-
-  // Implemented by each platform.  This message loop should be an IO message
-  // loop.
-  static NatPolicy* Create(
-      scoped_refptr<base::SingleThreadTaskRunner> task_runner);
-
- protected:
-  virtual void StartWatchingInternal() = 0;
-  virtual void StopWatchingInternal() = 0;
-  virtual void Reload() = 0;
-
-  // Used to check if the class is on the right thread.
-  bool OnPolicyThread() const;
-
-  // Takes the policy dictionary from the OS specific store and extracts the
-  // NAT traversal setting.
-  void UpdateNatPolicy(base::DictionaryValue* new_policy);
-
-  // Used for time-based reloads in case something goes wrong with the
-  // notification system.
-  void ScheduleFallbackReloadTask();
-  void ScheduleReloadTask(const base::TimeDelta& delay);
-
-  static const char kNatPolicyName[];
-
- private:
-  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
-
-  NatEnabledCallback nat_enabled_cb_;
-  bool current_nat_enabled_state_;
-  bool first_state_published_;
-
-  // Allows us to cancel any inflight FileWatcher events or scheduled reloads.
-  base::WeakPtrFactory<NatPolicy> weak_factory_;
-};
-
-}  // namespace policy_hack
-}  // namespace remoting
-
-#endif  // REMOTING_HOST_POLICY_HACK_NAT_POLICY_H_