Force disconnect all service clients when VM is shutting down

runtime/bin/vmservice/server.dart

Index: runtime/bin/vmservice/server.dart
diff --git a/runtime/bin/vmservice/server.dart b/runtime/bin/vmservice/server.dart
index a672bf23ce7aaa3787b77ae84e5455ed0e45b719..34d57158032e8e15162069b1860d7af2a489ca6f 100644
--- a/runtime/bin/vmservice/server.dart
+++ b/runtime/bin/vmservice/server.dart
@@ -16,6 +16,12 @@ class WebSocketClient extends Client {
     socket.done.then((_) => close());
   }
 
+  disconnect() {
+    if (socket != null) {
+      socket.close();
+    }
+  }
+
   void onWebSocketMessage(message) {
     if (message is String) {
       var map;
@@ -68,6 +74,11 @@ class HttpRequestClient extends Client {
   HttpRequestClient(this.request, VMService service)
       : super(service, sendEvents:false);
 
+  disconnect() {
+    request.response.close();
+    close();
+  }
+
   void post(String result) {
     if (result == null) {
       close();