Make sure BlobEvent is class.

Author: yilinwei

dom/src/main/scala/org/scalajs/dom/BlobEvent.scala

@@ -1,11 +1,20 @@
 package org.scalajs.dom
 
 import scala.scalajs.js
+import scala.scalajs.js.annotation._
 
 /** The AnimationEvent interface represents events providing information related to animations. */
+@JSGlobal
 @js.native
-trait BlobEvent extends Event {
+class BlobEvent(typeArg: String, init: js.UndefOr[BlobEventInit]) extends Event(typeArg, init) {
 
-  def data: Blob = js.native
+  def this(typeArg: String) = {
+    this(typeArg, js.undefined)
+  }
 
+  def this() = {
+    this("dataavailable", js.undefined)
+  }
+
+  val data: Blob = js.native
 }

dom/src/main/scala/org/scalajs/dom/BlobEventInit.scala

@@ -0,0 +1,8 @@
+package org.scalajs.dom
+
+import scala.scalajs.js
+
+@js.native
+trait BlobEventInit extends EventInit {
+  var data: js.UndefOr[Blob]
+}