[Tizen] Integrate WebMediaPlayer with Tizen Audio Session Manager

Integrate WebMediaPlayer with Tizen Audio Session Manager, so that the
policy framework can handle the media playback based on the priority of audio
stream.

This branch includes common classes and Chromium side changes that are
needed for integrating WebMediaPlayer with the Tizen Audio Session Manager.
Tizen provides Audio Session Manager library, which is used to register
and communicate playback status between WebMediaPlayer and Audio Session
Manager. 

The WebMediaPlayer executes in the Renderer -- as such, it does not have
direct native access. So, the WebMediaPlayer requests browser process to
register to the Tizen Audio Session Manager and define the audio session
type. For example, WebMediaPlayer control operations(play/pause) are
communicated with the BrowserMediaPlayerManager object in the browser
process through proxy. BrowserMediaPlayerManager in the browser process
receives control operations, and forwards them to corresponding
AudioSessionManager object. Callbacks from AudioSessionManager
object are converted to IPCs and then sent to the WebMediaPlayer in the
render process.