Support merged Dart-JS callstacks

LayoutTests/dart/inspector/merged-callstack.dart

+library merged_callstack_test;
+
+import 'dart:core' as core; // import with prefix so global dart:core fields don't appear in scope chain.
+import 'dart:html' as html; // import with prefix so global dart:html fields don't appear in scope chain.
+import 'dart:js' as js;     // import with prefix so global dart:js fields don't apppear in scope chain.
+
+main() {
+  html.window.onMessage.listen(handleMessage);
+}
+
+handleMessage(event) {
+  if (event.data == 'fromJS') {
+    bounceDart(10);
+  }
+}
+
+bounceHelperDart(core.int count) {
+  js.context.callMethod("bounce", [count-1, bounceDart]);
+}
+
+bounceDart(core.int count) {
+  if (count > 0) {
+    core.Function.apply(bounceHelperDart, [count]);
+  } else {
+    html.window.postMessage('fromDart', '*');
+  }
+}