Addition of AnalysisServer.isSocketOpen for clients to know if the server is still running.

editor/tools/plugins/com.google.dart.server/src/com/google/dart/server/AnalysisServerSocket.java

 /*
  * Copyright (c) 2014, the Dart project authors.
  * 
  * Licensed under the Eclipse Public License v1.0 (the "License"); you may not use this file except
  * in compliance with the License. You may obtain a copy of the License at
  * 
  * http://www.eclipse.org/legal/epl-v10.html
  * 
  * Unless required by applicable law or agreed to in writing, software distributed under the License
  * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
@@ skipping 22 matching lines @@
    * Return the request sink.
    */
   RequestSink getRequestSink();
 
   /**
    * Return the response stream.
    */
   ResponseStream getResponseStream();
 
   /**
+   * Return {@code true} if the socket is open.
+   */
+  boolean isOpen();
+
+  /**
    * Start the remote server and initialize request sink and response stream.
    */
   void start() throws Exception;
 
   /**
    * Stop the remote server.
    */
   void stop();
 }