[Telemetry] Re-enable page cyclers on mac.

The disk cache bug that was causing them to hang has been fixed.

BUG=306727

Review URL: https://codereview.chromium.org/30643002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237853 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237853