Revert 239236 "Disable media.tough_media_cases on Win8"

The CL did not actually disable the tests.

> Disable media.tough_media_cases on Win8
> 
> BUG=326384
> NOTRY=true
> 
> Review URL: https://codereview.chromium.org/108583002

TBR=shadi@chromium.org

Review URL: https://codereview.chromium.org/111953006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239957 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239957