[Media Router] Clean up issues related code.

chrome/browser/media/router/issue_manager.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_ISSUE_MANAGER_H_
 #define CHROME_BROWSER_MEDIA_ROUTER_ISSUE_MANAGER_H_
 
 #include <stddef.h>
 
 #include <vector>
@@ skipping 41 matching lines @@
   // Does not assume ownership of |observer|.
   // |observer|: IssuesObserver to be registered.
   void RegisterObserver(IssuesObserver* observer);
 
   // Unregisters |observer| from |issues_observers_|.
   // |observer|: IssuesObserver to be unregistered.
   void UnregisterObserver(IssuesObserver* observer);
 
  private:
   // Checks if the current top issue has changed. Updates |top_issue_|.
-  // If |top_issue_| has changed, issues in |issues_observers_| will be
+  // If |top_issue_| has changed, observers in |issues_observers_| will be
   // notified of the new top issue.
   void MaybeUpdateTopIssue();
 
   std::vector<Issue> issues_;
 
   // IssueObserver insteances are not owned by the manager.
   base::ObserverList<IssuesObserver> issues_observers_;
 
-  // The ID of the current top issue.
-  Issue::Id top_issue_id_;
+  // Pointer to the top Issue in |issues_|, or null if there are no Issues.
+  const Issue* top_issue_;

[mark a. foltz, 2016/07/27 18:52:04]

Consider base::Optional<Issue>.

[imcheng, 2016/09/13 20:27:54]

Keeping this as a pointer so we don't have to copy construct an extra Issue.

 
   DISALLOW_COPY_AND_ASSIGN(IssueManager);
 };
 
 }  // namespace media_router
 
 #endif  // CHROME_BROWSER_MEDIA_ROUTER_ISSUE_MANAGER_H_