Fix get_vm_timeline_rpc_test

runtime/observatory/tests/service/get_vm_timeline_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=--error_on_bad_type --error_on_bad_override --complete_timeline
 
 import 'dart:developer';
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 
 import 'test_helper.dart';
@@ skipping 28 matching lines @@
       continue;
     }
     if (event['name'] == 'Runnable' && event['ph'] == 'i') {
       // Skip Runnable events which don't have an isolate.
       continue;
     }
     if (event['cat'] == 'VM') {
       // Skip VM category events which don't have an isolate.
       continue;
     }
+    if (event['cat'] == 'API') {
+      // Skip API category events which sometimes don't have an isolate.
+      continue;
+    }
     Map arguments = event['args'];
     expect(arguments, new isInstanceOf<Map>());
     expect(arguments['isolateNumber'], new isInstanceOf<String>());
   }
 }
 
 var tests = [
   (VM vm) async {
     Map result = await vm.invokeRpcNoUpgrade('_getVMTimeline', {});
     expect(result['type'], equals('_Timeline'));
     expect(result['traceEvents'], new isInstanceOf<List>());
     List<Map> dartEvents = filterForDartEvents(result['traceEvents']);
     expect(dartEvents.length, equals(5));
     allEventsHaveIsolateNumber(dartEvents);
     allEventsHaveIsolateNumber(result['traceEvents']);
     expect(eventsContains(dartEvents, 'I', 'ISYNC'), isTrue);
     expect(eventsContains(dartEvents, 'X', 'apple'), isTrue);
     expect(eventsContains(dartEvents, 'b', 'TASK1'), isTrue);
     expect(eventsContains(dartEvents, 'e', 'TASK1'), isTrue);
     expect(eventsContains(dartEvents, 'n', 'ITASK'), isTrue);
     expect(eventsContains(dartEvents, 'q', 'ITASK'), isFalse);
   },
 ];
 
 main(args) async => runVMTests(args, tests, testeeBefore: primeTimeline);