GTK: minor MenuBarHelper fix.
GTK: minor MenuBarHelper fix.

If one of the buttons is not realized, gtk_widget_translate_coordinates() will fail on it. Instead of aborting, just skip to the next button. This can happen when opening a new window with a bookmark bar that doesn't have an overflow chevron (when the chevron has not been shown, it will be unrealized).

BUG=51810
TESt=see bug + above description

Review URL: http://codereview.chromium.org/3175006

git-svn-id: dd90618784b6a4b323ea0c23a071cb1c9e6f2ac7@55799 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