Revert 228557 "Disable DesktopCaptureApiTest on ChromeOS"

Tests should pass on ChromeOS after r228596

> Disable DesktopCaptureApiTest on ChromeOS
> 
> BUG=134249
> R=mallinath@chromium.org
> 
> Review URL: https://codereview.chromium.org/27268002

TBR=sergeyu@chromium.org

Review URL: https://codereview.chromium.org/27298002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228635 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228635