Optional binary payloads in VM service events.

runtime/bin/vmservice/observatory/lib/service_html.dart

Index: runtime/bin/vmservice/observatory/lib/service_html.dart
===================================================================
--- runtime/bin/vmservice/observatory/lib/service_html.dart	(revision 39330)
+++ runtime/bin/vmservice/observatory/lib/service_html.dart	(working copy)
@@ -7,6 +7,7 @@
 import 'dart:async';
 import 'dart:convert';
 import 'dart:html';
+import 'dart:typed_data';
 
 import 'package:observatory/service_common.dart';
 
@@ -37,6 +38,14 @@
   void close() {
     _webSocket.close();
   }
+  
+  Future<ByteData> nonStringToByteData(dynamic data) {
+    assert(data is Blob);
+    FileReader fileReader = new FileReader();
+    fileReader.readAsArrayBuffer(data);
+    return fileReader.onLoadEnd.first.then((e)
+        => new ByteData.view(fileReader.result));
+  }
 }
 
 /// The [WebSocketVM] communicates with a Dart VM over WebSocket. The Dart VM