Rework error handling in the service protocol and in Observatory.

runtime/observatory/tests/service/get_allocation_profile_rpc_test.dart

 // Copyright (c) 2015, 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.
 // VMOptions=--compile-all --error_on_bad_type --error_on_bad_override
 
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 
 import 'test_helper.dart';
 
@@ skipping 42 matching lines @@
     expect(result['heaps']['new']['type'], equals('HeapSpace'));
     expect(result['heaps']['old']['type'], equals('HeapSpace'));
     expect(result['members'].length, isPositive);
     expect(result['members'][0]['type'], equals('ClassHeapStats'));
   },
 
   (Isolate isolate) async {
     var params = {
       'reset' : 'banana',
     };
-    var result = await isolate.invokeRpcNoUpgrade(
-        '_getAllocationProfile', params);
-    expect(result['type'], equals('Error'));
-    expect(result['message'], contains("invalid 'reset' parameter"));
+    bool caughtException;
+    try {
+      await isolate.invokeRpcNoUpgrade('_getAllocationProfile', params);
+      expect(false, isTrue, reason:'Unreachable');
+    } on ServerRpcException catch (e) {
+      caughtException = true;
+      expect(e.code, equals(ServerRpcException.kInvalidParams));
+      expect(e.data['details'],
+             "_getAllocationProfile: invalid \'reset\' parameter: banana");
+    }
+    expect(caughtException, isTrue);
   },
 
   (Isolate isolate) async {
     var params = {
       'gc' : 'banana',
     };
-    var result = await isolate.invokeRpcNoUpgrade(
-        '_getAllocationProfile', params);
-    expect(result['type'], equals('Error'));
-    expect(result['message'], contains("invalid 'gc' parameter"));
+    bool caughtException;
+    try {
+      await isolate.invokeRpcNoUpgrade(
+          '_getAllocationProfile', params);
+      expect(false, isTrue, reason:'Unreachable');
+    } on ServerRpcException catch (e) {
+      caughtException = true;
+      expect(e.code, equals(ServerRpcException.kInvalidParams));
+      expect(e.data['details'],
+             "_getAllocationProfile: invalid \'gc\' parameter: banana");
+    }
+    expect(caughtException, isTrue);
   },
 ];
 
 main(args) async => runIsolateTests(args, tests);