allow client to specify any combination of add/modified/removed

pkg/analysis_server/lib/src/protocol.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library protocol;
 
 import 'dart:convert' show JsonDecoder;
 
 /**
  * Instances of the class [Request] represent a request that was received.
@@ skipping 167 matching lines @@
           "be a map"));
     }
     if (!datum.containsKey(key)) {
       throw new RequestFailure(new Response.invalidParameter(request, path,
           "contain key '$key'"));
     }
     return new RequestDatum(request, "$path.$key", datum[key]);
   }
 
   /**
+   * Return `true` if the datum is a Map containing the given [key].
+   */
+  bool hasKey(String key) {
+    if (datum is! Map<String, dynamic>) {
+      throw new RequestFailure(new Response.invalidParameter(request, path,
+          "be a map"));
+    }
+    return datum.containsKey(key);
+  }
+
+  /**
    * Validate that the datum is a Map whose keys are strings, and call [f] on
    * each key/value pair in the map.
    */
   void forEachMap(void f(String key, RequestDatum value)) {
     if (datum is! Map<String, dynamic>) {
       throw new RequestFailure(new Response.invalidParameter(request, path,
           "be a map"));
     }
     datum.forEach((String key, dynamic value) {
       f(key, new RequestDatum(request, "$path.$key", value));
@@ skipping 495 matching lines @@
   /**
    * The response to be returned as a result of the failure.
    */
   final Response response;
 
   /**
    * Initialize a newly created exception to return the given reponse.
    */
   RequestFailure(this.response);
 }