tab capture: Change the permissions for tabs.captureVisibleTab().

Require an extension to have '<all_urls>' permission, or been granted the
'activeTab' permission to be allowed to use tabs.captureVisibleTab().

BUG=83432
R=kalman@chromium.org

Review URL: https://codereview.chromium.org/140433003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246766 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246766