update error handling to send response with stack trace

pkg/analysis_server/test/protocol_test.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.protocol;
 
 import 'dart:convert';
 
 import 'package:analysis_server/src/constants.dart';
 import 'package:analysis_server/src/protocol.dart';
@@ skipping 87 matching lines @@
     RequestError error = new RequestError(RequestErrorCode.INVALID_REQUEST, 'msg');
     expect(error.code, RequestErrorCode.INVALID_REQUEST);
     expect(error.message, "msg");
     expect(error.toJson(), equals({
       CODE: 'INVALID_REQUEST',
       MESSAGE: "msg"
     }));
   }
 
   void test_fromJson() {
+    var trace = 'a stack trace\r\nfoo';
     var json = {
       CODE: RequestErrorCode.INVALID_PARAMETER.name,
       MESSAGE: 'foo',
-      DATA: {
-        'ints': [1, 2, 3]
-      }
+      STACK_TRACE: trace
     };
     RequestError error = new RequestError.fromJson(new ResponseDecoder(null), '',
         json);
     expect(error.code, RequestErrorCode.INVALID_PARAMETER);
     expect(error.message, "foo");
-    expect(error.data['ints'], [1, 2, 3]);
+    expect(error.stackTrace, trace);
   }
 
   void test_toJson() {
+    var trace = 'a stack trace\r\nbar';
     RequestError error = new RequestError(
-        RequestErrorCode.UNKNOWN_REQUEST, 'msg', data: {});
-    error.data['answer'] = 42;
-    error.data['question'] = 'unknown';
+        RequestErrorCode.UNKNOWN_REQUEST, 'msg', stackTrace: trace);
     expect(error.toJson(), {
       CODE: 'UNKNOWN_REQUEST',
       MESSAGE: 'msg',
-      DATA: {
-        'answer': 42,
-        'question': 'unknown'
-      }
+      STACK_TRACE: trace
     });
   }
 }
 
 
 @ReflectiveTestCase()
 class RequestTest {
   void test_fromJson() {
     Request original = new Request('one', 'aMethod');
     String json = JSON.encode(original.toJson());
@@ skipping 112 matching lines @@
 
   void test_fromJson_withResult() {
     Response original = new Response('myId', result: {'foo': 'bar'});
     Response response = new Response.fromJson(original.toJson());
     expect(response.id, equals('myId'));
     Map<String, Object> result = response.toJson()['result'];
     expect(result.length, equals(1));
     expect(result['foo'], equals('bar'));
   }
 }