Adding a logging class to cast. 
This cl is first in a series - follow-up cl's will include using this class in Cast and performing data analysis.

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=229984

Review URL: https://codereview.chromium.org/26909002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230181 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230181