GitLab

This CL adds the Blink classes needed for implementing
MediaRecorder API and two tests.This API allows for
recording a MediaStream, i.e. a local or remote feed of 
live media(s). This CL does not include a BlobEvent to
communicate recorded data to JS.

See DD @ https://goo.gl/vSjzC5 (*) for the plan and
https://codereview.chromium.org/1211973012/ for a
hack of all Chrome parts.

(*) Used to be https://goo.gl/kreaQj

BUG=262211

Review URL: https://codereview.chromium.org/1255873002

git-svn-id: svn://svn.chromium.org/blink/trunk@201727 bbb929c8-8fbe-4397-9dbb-9b2b20218538