Allow stepping when paused at isolate start.

runtime/observatory/tests/service/pause_on_start_and_exit_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';
+import 'dart:async';
+
+void testMain() {
+  print('Hello');
+}
+
+var tests = [
+
+(Isolate isolate) async {
+  Completer completer = new Completer();
+  var stream = await isolate.vm.getEventStream(VM.kDebugStream);
+  var subscription;
+  subscription = stream.listen((ServiceEvent event) {
+    if (event.kind == ServiceEvent.kPauseStart) {
+      print('Received PauseStart');
+      subscription.cancel();
+      completer.complete();
+    }
+  });
+
+  if (isolate.pauseEvent != null &&
+      isolate.pauseEvent.kind == ServiceEvent.kPauseStart) {
+    // Wait for the isolate to hit PauseStart.
+    subscription.cancel();
+  } else {
+    await completer.future;
+  }
+
+  completer = new Completer();
+  stream = await isolate.vm.getEventStream(VM.kDebugStream);
+  subscription = stream.listen((ServiceEvent event) {
+    if (event.kind == ServiceEvent.kPauseExit) {
+      print('Received PauseExit');
+      subscription.cancel();
+      completer.complete();
+    }
+  });
+
+  print('Resuming...');
+  isolate.resume();
+
+  // Wait for the isolate to hit PauseExit.
+  await completer.future;
+},
+
+];
+
+main(args) => runIsolateTests(args, tests,
+                              testeeConcurrent: testMain,
+                              pause_on_start: true, pause_on_exit: true);