[chromedriver] Add a python test to verify chromedriver.log is not empty.

BUG=chromedriver:638
NOTRY=true

Review URL: https://codereview.chromium.org/144303003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246192 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246192