Add media router common classes and unittests.

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 <string>
+
+namespace media_router {
+
+class MediaSource {
+ public:
+  MediaSource() = default;
+  MediaSource(const MediaSource& other) = default;
+  virtual ~MediaSource();

[xhwang, 2015/03/09 17:37:31]

Is MediaSources a base class? Wondering whether we need "virtual".

[Kevin M, 2015/03/09 23:32:06]

Done.

[Kevin M, 2015/03/09 23:32:06]

Done.

+
+  // Static creation methods for various media types.
+  static MediaSource ForTab(int tab_id);
+  static MediaSource ForDesktop();
+  static MediaSource ForCastApp(const std::string& app_id);
+  static MediaSource ForPresentationUrl(const std::string& presentation_url);
+
+  // Sets the ID of a MediaSource object to |id| if it is valid.
+  // Returns true if |id| is valid and the MediaSource is modified.
+  // Returns false and leaves the MediaSource untouched if |id| is invalid.
+  bool Parse(const std::string& id);

[xhwang, 2015/03/09 17:37:31]

Hmm, the default ctor and this function provide another way to create a
MediaSource. In which case should we prefer this to the four static For* methods
above? Should the caller make sure the |id| is valid? Someone looking at this
class may wonder whether he/she should use ForCastApp(), or MediaSource() +
Parse()...

[Kevin M, 2015/03/09 23:32:06]

I agree that this is unclear. I've moved the creation methods into a standalone
.cc/.h along with a comment that proposes that we move them out of c/b/m/r
entirely, since all but one are meant to be invoked by the UI only. The class is
much more basic now.

+
+  // Gets the ID of the media source.
+  const std::string& id() const;
+
+  // Checks if the media source uses display mirroring.
+  bool SupportsMirroring() const;
+
+ protected:
+  explicit MediaSource(const std::string& source_id);
+
+ private:
+  static bool IsValid();

[xhwang, 2015/03/09 17:37:31]

not defined?

[Kevin M, 2015/03/09 23:32:06]

Acknowledged.

+
+  std::string id_;
+};
+
+}  // namespace media_router
+
+#endif  // CHROME_BROWSER_MEDIA_ROUTER_MEDIA_SOURCE_H_