[Media Router] Clean up issues related code.

chrome/browser/media/router/issues_observer.h

 // Copyright 2015 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 CHROME_BROWSER_MEDIA_ROUTER_ISSUES_OBSERVER_H_
 #define CHROME_BROWSER_MEDIA_ROUTER_ISSUES_OBSERVER_H_
 
 #include "base/macros.h"
 #include "chrome/browser/media/router/issue.h"
 
 namespace media_router {
 
 class MediaRouter;
 
 // Base class for observing Media Router Issue. There is at most one Issue
 // at any given time.
 class IssuesObserver {
  public:
   explicit IssuesObserver(MediaRouter* router);
   virtual ~IssuesObserver();
 
-  void RegisterObserver();
-  void UnregisterObserver();
+  // Registers with Media Router to start observing for Issues. No-ops if Init()
+  // has already been called before.
+  void Init();
 
   // Called when there is an updated Media Router Issue.
-  // If |issue| is nullptr, then there is currently no issue.
-  virtual void OnIssueUpdated(const Issue* issue) {}
+  // Note that |issue| is owned by the IssueManager that is calling the
+  // observers. Implementations that wish to retain the data must make a copy
+  // of |issue|.
+  virtual void OnIssue(const Issue& issue) {}
+
+  // Called when there are no more issues.
+  virtual void OnIssuesCleared() {}
 
  private:
   MediaRouter* router_;
+  bool initialized_;
 
   DISALLOW_COPY_AND_ASSIGN(IssuesObserver);
 };
 
 }  // namespace media_router
 
 #endif  // CHROME_BROWSER_MEDIA_ROUTER_ISSUES_OBSERVER_H_