[PPAPI] Refine Configure() for Pepper MediaStream API.

BUG=330851

Review URL: https://codereview.chromium.org/141993002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246697 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246697