Changed WebRTC logging to send log messages from renderer to browser side and write them to the buffer there.

Buffering is done on the renderer side so that IPC isn't overloaded.

As a side note, the design will be revisited soon; issue 333894.

BUG=332957
R=cdn@chromium.org, jochen@chromium.org, joi@chromium.org, vrk@chromium.org

Review URL: https://codereview.chromium.org/135403004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244965 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244965