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

pkg/analysis_server/lib/src/protocol.dart

Index: pkg/analysis_server/lib/src/protocol.dart
diff --git a/pkg/analysis_server/lib/src/protocol.dart b/pkg/analysis_server/lib/src/protocol.dart
index 7cdfa18de0c22eb00ea302288a470cda0cc29a96..1434073bf392068db86d2f91ca6eef1f782d6147 100644
--- a/pkg/analysis_server/lib/src/protocol.dart
+++ b/pkg/analysis_server/lib/src/protocol.dart
@@ -185,6 +185,13 @@ class RequestDatum {
   }
 
   /**
+   * Return `true` if the datum is a Map containing the given [key].
+   */
+  bool hasKey(String key) {
+    return datum is Map<String, dynamic> && datum.containsKey(key);

[Paul Berry, 2014/05/15 00:30:54]

This means that if we receive a datum from the client that has a non-map where a
map was expected, we will silently act like the datum was the empty map.

I'd prefer to generate an error in that case (as we do in operator[],
forEachMap, and asStringMap) so that we help detect bugs in the client.

[danrubel, 2014/05/15 11:48:44]

Good suggestion. Done.

+  }
+
+  /**
    * Validate that the datum is a Map whose keys are strings, and call [f] on
    * each key/value pair in the map.
    */