Prevent the default action on clicking on links on the Feedback app.
This prevents a new tab from opening if someone middle clicks on the system information or metrics link on the Feedback app.

R=xiyuan@chromium.org
BUG=342281
TEST=Middle clicking the system information link doesn't open a new tab in the background.

Review URL: https://codereview.chromium.org/182343006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253984 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253984