Files.app: grant access to other profiles' Files.app when new profile is added.

BUG=337705

Review URL: https://codereview.chromium.org/142223003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248998 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248998