Trim spaces from link label in drag bubble

Update the link drag bubble to trim leading and trailing spaces.

R=leviw@chromium.org
BUG=332149

Review URL: https://codereview.chromium.org/125113003

git-svn-id: svn://svn.chromium.org/blink/trunk@164617 bbb929c8-8fbe-4397-9dbb-9b2b20218538