Track all profiles ChromeVox loads to.

- keeps track of all profile event routers ChromeVox registers observers on.
- ensures AccessibilityManager unregisters observers on all profile event routers when Shutdown occurs.
- always plays startup/shutdown sounds regardless of system preference. (This is the only accessible notification that ChromeVox has started/shutdown when toggling).

BUG=323030,322793
TEST=Manual.

Review URL: https://codereview.chromium.org/123443002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243249 0039d316-1c4b-4281-b951-d872f2087c98
Don't allow software fallback for UI compositor on CrOS

BUG=331847

Review URL: https://codereview.chromium.org/123463004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243250 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243250