GitLab

There is a small chance that the permission bubble manager for a given
web contents has been deleted before an asychronous permission request
has been handled.

BUG=371085

Review URL: https://codereview.chromium.org/282693002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@269987 0039d316-1c4b-4281-b951-d872f2087c98