Test showing crash when stepping through new Map creation.

runtime/observatory/tests/service/step_test.dart

Index: runtime/observatory/tests/service/step_test.dart
diff --git a/runtime/observatory/tests/service/step_test.dart b/runtime/observatory/tests/service/step_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..f73e1dc1f0a67dbff3642df1e09e5518890fd743
--- /dev/null
+++ b/runtime/observatory/tests/service/step_test.dart
@@ -0,0 +1,49 @@
+import 'dart:async';
+import 'test_helper.dart';
+import 'service_test_common.dart';
+import 'package:observatory/service_io.dart';
+import 'package:unittest/unittest.dart';
+
+const int LINE_A = 10;
+
+code() {
+  var x = {}; // LINE_A
+}
+
+Future<Isolate> stepThroughProgram(Isolate isolate) async {
+  Completer completer = new Completer();
+  int pauseEventsSeen = 0;
+  isolate.vm.getEventStream(VM.kDebugStream).then((stream) {

[Cutch, 2016/11/09 14:48:49]

Have you considered using helper routines from service_test_common.dart ?

+    stream.listen((ServiceEvent event) {
+      if (event.kind == ServiceEvent.kPauseBreakpoint) {
+        // We are paused: Step further.
+        pauseEventsSeen++;
+        isolate.stepInto();
+      } else if (event.kind == ServiceEvent.kPauseExit) {
+        // We are at the exit: The test is done.
+        expect(pauseEventsSeen > 20, true,
+            reason: "Saw only $pauseEventsSeen pause events.");
+        completer.complete();
+      }
+    });
+  });
+
+  // We expect to start paused.
+  expect(isEventOfKind(isolate.pauseEvent, ServiceEvent.kPauseStart), true);

[Cutch, 2016/11/09 14:48:49]

It's possible that the isolate hasn't paused at start yet. This will likely
flake on the bots. See the helper routine `hasPausedAtStart` for a race free
version.

+
+  // Set breakpoint at the "var x = {};" line.
+  var rootLib = isolate.rootLibrary;
+  await rootLib.load();
+  isolate.addBreakpoint(rootLib.scripts[0], LINE_A);
+
+  // Resume (and step on every pause via the event stream listener above).
+  isolate.resume();
+
+  // The test is done once the completer is complete.
+  return completer.future;
+}
+
+var tests = [stepThroughProgram];
+
+main(args) => runIsolateTestsSynchronous(args, tests,
+    testeeConcurrent: code, pause_on_start: true, pause_on_exit: true);