Clear an error message from the throbber space.
Clear an error message from the throbber space.

When an update fails, we display an error string and allow the
user to try again by manually pressing the update button. When
the user does that, we should clear the error message so that the
update throbber doesn't draw over the text, which looks ugly.

BUG=19272 (http://crbug.com/19272)
TEST=Difficult to repro: try to update chrome and fail, press the
     update button and notice that the error message disappears when
     the throbber is active.
Review URL: http://codereview.chromium.org/165462

git-svn-id: http://src.chromium.org/svn/trunk/src@23329 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 3fc2ab691f8f99349de9475cdeff5c9a529cc2a7
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