Rework "analysis.updateContent" analysis server request.

pkg/analysis_server/test/integration/integration_tests.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 test.integration.analysis;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:convert';
 import 'dart:io';
@@ skipping 552 matching lines @@
           String id = message['id'];
           Completer completer = _pendingCommands[id];
           if (completer == null) {
             fail('Unexpected response from server: id=$id');
           } else {
             _pendingCommands.remove(id);
           }
           if (messageAsMap.containsKey('error')) {
             // TODO(paulberry): propagate the error info to the completer.
             completer.completeError(new UnimplementedError(
-                'Server responded with an error'));
+                'Server responded with an error: ${JSON.encode(message)}'));
           } else {
             completer.complete(messageAsMap['result']);
           }
           // Check that the message is well-formed.  We do this after calling
           // completer.complete() or completer.completeError() so that we don't
           // stall the test in the event of an error.
           expect(message, isResponse);
         } else {
           // Message is a notification.  It should have an event and possibly
           // params.
@@ skipping 106 matching lines @@
    */
   void _recordStdio(String line) {
     double elapsedTime = _time.elapsedTicks / _time.frequency;
     line = "$elapsedTime: $line";
     if (_debuggingStdio) {
       print(line);
     }
     _recordedStdio.add(line);
   }
 }