[Mac] Cancel obsolete autoClose calls in DownloadShelfController.

If pending autoClose calls aren't cancelled when the shelf is being
removed, the pending call may be invoked after the view has been
destroyed.

When new download items are added, it should also cancel pending
autoClose calls, since the shelf should stay open for the new item.

BUG=234314

Review URL: https://chromiumcodereview.appspot.com/14358017

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@195985 0039d316-1c4b-4281-b951-d872f2087c98
3 files changed