mac: Fix a history swiper bug with magic mouse.
Canceling a history swipe with the magic mouse would fail to hide the swipe
arrow. Previously, the arrow was dismissed in `dealloc`, and I moved the
animation to `dismiss` in a previous change (
107343008). Unfortunately, the
logic for magic mouse history swiping was failing to call `dismiss` if the
history swipe was cancelled.
BUG=330312
Review URL: https://codereview.chromium.org/
115693012
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243417 0039d316-1c4b-4281-b951-d872f2087c98