WebUI: Fix middle click link issue in click handler
WebUI: Fix middle click link issue in click handler

This makes sure we do not open a link twice (once due to the handler and once
due to the browser behavior).

BUG=Evan?
TEST=Evan?

Review URL: http://codereview.chromium.org/6250207

git-svn-id: http://src.chromium.org/svn/trunk/src@75149 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: f2d24ddf0d6f2eacb09e1ea3133d3d0a73bccb5a
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