Add a diagnostic.getServerPort analysis server request.

pkg/analysis_server/lib/plugin/protocol/protocol.dart

Index: pkg/analysis_server/lib/plugin/protocol/protocol.dart
diff --git a/pkg/analysis_server/lib/plugin/protocol/protocol.dart b/pkg/analysis_server/lib/plugin/protocol/protocol.dart
index 49e19c16fbc0aa3b245e8664011fe8ad12398803..bec501d006e2e0020796f19f02020a85ac7be3b7 100644
--- a/pkg/analysis_server/lib/plugin/protocol/protocol.dart
+++ b/pkg/analysis_server/lib/plugin/protocol/protocol.dart
@@ -543,6 +543,15 @@ class Response {
    * Initialize a newly created instance to represent an error condition caused
    * by a [request] that cannot be handled by any known handlers.
    */
+  Response.errorHandlingRequest(Request request, dynamic error)
+      : this(request.id,
+            error: new RequestError(
+                RequestErrorCode.ERROR_HANDLING_REQUEST, '$error'));
+
+  /**
+   * Initialize a newly created instance to represent an error condition caused
+   * by a [request] that cannot be handled by any known handlers.
+   */
   Response.unknownRequest(Request request)
       : this(request.id,
             error: new RequestError(