[AudioPlayer] Re-enable the tests of audio player.

Some test was flaky but it has been fixed, so we re-enable the tests.

BUG=340955
TEST=browser_tests passes.
TBR=hirono@chromium.org

Review URL: https://codereview.chromium.org/163203003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252887 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252887