Allow stepping when paused at isolate start.

runtime/observatory/tests/service/isolate_lifecycle_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 'dart:async';
 import 'dart:isolate' as I;
 
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
@@ skipping 22 matching lines @@
 int numPaused(vm) {
   int paused = 0;
   for (var isolate in vm.isolates) {
     if (isolate.paused) {
       paused++;
     }
   }
   return paused;
 }
 
-int numRunning(vm) {
-  int running = 0;
-  for (var isolate in vm.isolates) {
-    if (!isolate.paused) {
-      running++;
-    }
-  }
-  return running;
-}
-
 var tests = [
   (VM vm) async {
-    // Wait for the testee to start all of the isolates.
-    if (vm.isolates.length != spawnCount + 1) {
-      await processServiceEvents(vm, VM.kIsolateStream,
-                                 (event, sub, completer) {
+    Completer completer = new Completer();
+    var stream = await vm.getEventStream(VM.kIsolateStream);
+    if (vm.isolates.length < spawnCount + 1) {
+      var subscription;
+      subscription = stream.listen((ServiceEvent event) {
         if (event.kind == ServiceEvent.kIsolateStart) {
-          if (vm.isolates.length == spawnCount + 1) {
-            sub.cancel();
+          if (vm.isolates.length == (spawnCount + 1)) {
+            subscription.cancel();
             completer.complete(null);
           }
         }
       });
+      await completer.future;
     }
     expect(vm.isolates.length, spawnCount + 1);
   },
 
   (VM vm) async {
     // Load each isolate.
     for (var isolate in vm.isolates) {
       await isolate.load();
     }
   },
 
   (VM vm) async {
-    // Wait for all spawned isolates to hit pause-at-exit.
-    if (numPaused(vm) != spawnCount) {
-      await processServiceEvents(vm, VM.kDebugStream,
-                                 (event, sub, completer) {
+    Completer completer = new Completer();
+    var stream = await vm.getEventStream(VM.kDebugStream);
+    if (numPaused(vm) < spawnCount) {
+      var subscription;
+      subscription = stream.listen((ServiceEvent event) {
         if (event.kind == ServiceEvent.kPauseExit) {
-          if (numPaused(vm) == spawnCount) {
-            sub.cancel();
+          if (numPaused(vm) == (spawnCount + 1)) {
+            subscription.cancel();
             completer.complete(null);
           }
         }
       });
+      await completer.future;
     }
-    expect(numPaused(vm), spawnCount);
-    expect(numRunning(vm), 1);
+    expect(numPaused(vm), spawnCount + 1);
   },
 
 
   (VM vm) async {
     var resumedReceived = 0;
-    var eventsDone = processServiceEvents(vm, VM.kIsolateStream,
-                                          (event, sub, completer) {
+    Completer completer = new Completer();
+    var stream = await vm.getEventStream(VM.kIsolateStream);
+    var subscription;
+    subscription = stream.listen((ServiceEvent event) {
       if (event.kind == ServiceEvent.kIsolateExit) {
         resumedReceived++;
-        if (resumedReceived == resumeCount) {
-          sub.cancel();
+        if (resumedReceived >= resumeCount) {
+          subscription.cancel();
           completer.complete(null);
         }
       }
     });
+
+    // Resume a subset of the isolates.
     var resumesIssued = 0;
     var isolateList = vm.isolates.toList();
     for (var isolate in isolateList) {
       if (isolate.name.endsWith('main')) {
         continue;
       }
       try {
         resumesIssued++;
         await isolate.resume();
       } catch(_) {}
       if (resumesIssued == resumeCount) {
         break;
       }
     }
-    return eventsDone;
+    await completer.future;
   },
 
   (VM vm) async {
-    expect(numPaused(vm), spawnCount - resumeCount);
-    expect(numRunning(vm), 1);
+    expect(numPaused(vm), spawnCount + 1 - resumeCount); 
   },
 ];
 
 main(args) async => runVMTests(args, tests,
                                testeeBefore: before,
                                testeeConcurrent: during,
                                pause_on_exit: true);