Check for WebContents capturers when reporting output link types.

Adds a PP_OutputProtectionLinkType_Private flag which is set on the
link mask returned by PPB_OutputProtection_Private::QueryStatus().

PPB_OutputProtection_Private clients can now check if a capturer
is attached to the given WebContents.

BUG=272269
TEST=none

Review URL: https://codereview.chromium.org/26255006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228306 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228306