Fix AppListServiceMacInteractiveTest.ShowAppListUsingShim on Snow Leopard and re-enable.

Threaded animations are crashy on Snow Leopard. Since there's not much
test coverage for Lion either, this CL falls back to non-threaded
animations for Snow Leopard and Lion for showing the Mac App Launcher.

BUG=335550

Review URL: https://codereview.chromium.org/142873002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245977 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245977