Better error message when tools/sync-webkit-git.py is run from wrong dir.
Better error message when tools/sync-webkit-git.py is run from wrong dir.

Contributed by Hans Wennborg <hans@chromium.org>.

BUG=41695
TEST=Ran the script from different dirs to cover all paths through affected code.

Review URL: http://codereview.chromium.org/1582033

git-svn-id: http://src.chromium.org/svn/trunk/src@44921 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 25aedaa5407d594c9dd8cc2533bd0d92bdd1a1d2
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser