MediaRecorder: Adding BlobEvent and connecting it in MediaRecorderHandler

Source/modules/mediarecorder/MediaRecorder.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#MediaRecorderAPI
 
 enum RecordingStateEnum { "inactive", "recording", "paused" };
 
 [
     GarbageCollected,
     ActiveDOMObject,
     // TODO(mcasas): consider changing |mimeType| to a dictionary with said key, see https://github.com/w3c/mediacapture-record/issues/19
+    // TODO(mcasas): Remove [TreatUndefinedAs], see https://github.com/w3c/mediacapture-record/issues/7
     Constructor(MediaStream stream, [TreatUndefinedAs=Missing] optional DOMString mimeType),
     ConstructorCallWith=ExecutionContext,
     RaisesException=Constructor,
     RuntimeEnabled=MediaRecorder
 ] interface MediaRecorder : EventTarget {
     readonly attribute MediaStream stream;
     readonly attribute DOMString mimeType;
     readonly attribute RecordingStateEnum state;
     attribute boolean ignoreMutedMedia;
 
     attribute EventHandler onstart;
     attribute EventHandler onstop;
     attribute EventHandler ondataavailable;
     attribute EventHandler onpause;
     attribute EventHandler onresume;
     attribute EventHandler onerror;
 
     [RaisesException] void start(optional long timeslice);
     [RaisesException] void stop();
     [RaisesException] void pause();
     [RaisesException] void resume();
     [RaisesException] void requestData();
 
     static DOMString canRecordMimeType(DOMString mimeType);
 };