Use webrtc::MouseCursorMonitor for cursor shapes

Use webrtc::MouseCursorMonitor for cursor shapes instead of
webrtc::VideoFrameCapturer, in preparation for deprecating cursor shape
functionality in the latter.

BUG=324033

Review URL: https://codereview.chromium.org/92473002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247689 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247689