[chromedriver] Capture server logs to a file.

BUG=chromedriver:592
R=kkania@chromium.org

Review URL: https://codereview.chromium.org/39143002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230774 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230774