Fixes painting of focus rect on download shelf

There were a couple of issues here:
. Focus rect wouldn't always draw. This is because DownloadShelfView
  was overriding OnWillChangeFocus to SchedulePaint the right
  regions. This doesn't work on first focus since AccessiblePane only
  adds itself as a FocusChangeListener after changing focus.
. Focus rect extended outside the bounds of the item, which looked
  bad.

By constraining the focus rect to the bounds of the button the code is
simplified and better matches what we do else where.

BUG=79396
TEST=none
R=dmazzoni@chromium.org

Review URL: https://codereview.chromium.org/110973003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239744 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239744
Add UBSan Linux runtime to the packaged Clang build.

BUG=174801
R=pbos@chromium.org, thakis@chromium.org

Review URL: https://codereview.chromium.org/108083003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239745 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239745