MediaRecorder: Adding BlobEvent and connecting it in MediaRecorderHandler

Source/modules/mediarecorder/BlobEvent.idl

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// https://w3c.github.io/mediacapture-record/MediaRecorder.html#blob-event
+
+[
+    // This constructor is yet to be added to the specification, see:
+    // https://github.com/w3c/mediacapture-record/issues/11
+    Constructor(DOMString type, optional BlobEventInit eventInit),
+    RuntimeEnabled=MediaRecorder
+]
+interface BlobEvent : Event {
+    readonly attribute Blob data;
+};