[Media Router] Design MediaRouter interface with stub implementation.

chrome/browser/media/router/media_source.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_MEDIA_SOURCE_H_
 #define CHROME_BROWSER_MEDIA_ROUTER_MEDIA_SOURCE_H_
 
+#include <ostream>
 #include <string>
 
 namespace media_router {
 
+using MediaSourceId = std::string;
+
 class MediaSource {
  public:
-  explicit MediaSource(const std::string& id);
+  explicit MediaSource(const MediaSourceId& id);
+  MediaSource();
   ~MediaSource();
 
   // Gets the ID of the media source.
-  std::string id() const;
+  MediaSourceId id() const;
+
+  // Returns true if two MediaSource objects use the same media ID.
+  bool Equals(const MediaSource& other) const;
+
+  // Returns true if a MediaSource is empty or uninitialized.
+  bool Empty() const;
+
+  // Used for logging.
+  std::string ToString() const;
 
  private:
-  std::string id_;
+  MediaSourceId id_;
+};
+
+// Inequality comparison functor to provide map lookup capabilities for
+// MediaSource.
+class MediaSourceLess {
+ public:
+  bool operator()(const MediaSource& lhs, const MediaSource& rhs) const {
+    return lhs.id() < rhs.id();

[xhwang, 2015/04/06 20:51:31]

Comparing strings isn't efficient. Consider using hash tables:
base/containers/hash_tables.h

[imcheng, 2015/04/06 21:54:20]

Replaced this class with a struct Hash.

+  }
 };
 
 }  // namespace media_router
 
 #endif  // CHROME_BROWSER_MEDIA_ROUTER_MEDIA_SOURCE_H_