[PPAPI] API definition for video media stream artifacts

This API follows the design at
https://docs.google.com/a/google.com/document/d/1rlwmFhf7VCX8mfrBok8wqXNgvr_ERhL2k6Fqha-pgIo/edit?disco=AAAAAHos8Y8#


It defines new objects for the consumption of media video tracks based on the private VideoSource/VideoDestination classes.

BUG=330851

Review URL: https://codereview.chromium.org/107083004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243099 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243099