cros_workon: Fix for chromeos-chrome in minilayout
cros_workon: Fix for chromeos-chrome in minilayout

The cros_workon script did not support chromeos-chrome in a
minilayout. This appears to result from the usual oddities of
chromeos-chrome and some assumptions in cros_workon's support for
CHROME_ORIGIN=GERRIT_SOURCE.

BUG=None
TEST=Tested on full and minilayout with x86-alex.
  cros_workon start and stop succeed, and both equery w and
  ~/trunk/.config/cros_workon/x86-alex show the correct behavior.

Change-Id: Ic239f08ebedc02e6faea36d54c46ae219bfeb044
Reviewed-on: https://gerrit.chromium.org/gerrit/16995
Reviewed-by: Mandeep Singh Baines <19acf4ef1f391f4aab404dc5703cac3632e06f3a@chromium.org>
Reviewed-by: Ryan Cui <5ce1592d53754a87a44fc2eb7b63d5f77cf50fdb@chromium.org>
Tested-by: Chris Wolfe <4f23406e03c8ffaccefe8744212d3543c02e8d87@chromium.org>
Commit-Ready: Chris Wolfe <4f23406e03c8ffaccefe8744212d3543c02e8d87@chromium.org>

mgireesh05/dev-util,marineam/coreos-dev-util,mgireesh05/dev-util,mgireesh05/dev-util,coreos/dev-util,marineam/coreos-dev-util,coreos/dev-util,coreos/dev-util