Specify branch when fetching in sync-webkit-git.py.
Specify branch when fetching in sync-webkit-git.py.

This allows the fetch to succeed even when the current WebKit branch has a
different remote than the magic gclient branch.

BUG=63850
TEST=none

Review URL: http://codereview.chromium.org/5185005

git-svn-id: dd90618784b6a4b323ea0c23a071cb1c9e6f2ac7@67565 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser