Cast: Added a LogSerializer class and hook it up to sender app.

A LogSerializer takes a FrameEventMap and PacketEventMap as well as a stream id associated with these events and outputs them in a serialized format. A LogSerializer is capable of taking more than one set of data (e.g. one set of audio + one set of video frame/packet events) before outputting the serialized data.

The intended use case is that at the end of a mirroring session, logged events will be passed to LogSerializer in order to obtain a serialized format to return to the application which can then be uploaded.

Review URL: https://codereview.chromium.org/166273010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252483 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252483