Add TabCaptureApiTest to ensure tabCapture works in split incognito mode.

Review URL: https://codereview.chromium.org/26320006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227681 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227681