Make root-zone handleUncaughtError rethrow with the correct stack.

sdk/lib/_internal/js_runtime/lib/async_patch.dart

Index: sdk/lib/_internal/js_runtime/lib/async_patch.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/async_patch.dart b/sdk/lib/_internal/js_runtime/lib/async_patch.dart
index f8412c1be549a41d274ab123fa242ab478cfbc9d..1155e79f76964886ed61ab0c2006b9ed1c5e292f 100644
--- a/sdk/lib/_internal/js_runtime/lib/async_patch.dart
+++ b/sdk/lib/_internal/js_runtime/lib/async_patch.dart
@@ -506,3 +506,8 @@ class _SyncStarIterable extends IterableBase {
 
   Iterator get iterator => new _SyncStarIterator(JS('', '#()', _outerHelper));
 }
+
+@patch
+void _rethrow(Object error, StackTrace stackTrace) {
+  throw new AsyncError(error, stackTrace);

[Ivan Posva, 2015/10/02 23:40:39]

This seems to differ significantly from the VM implementation. How come? Are we
really willing to have this entirely different behaviour between the two
implementations?

[Lasse Reichstein Nielsen, 2015/10/05 06:18:49]

I haven't found a way to throw an object *and* a stack-trace in JS.
Maybe there is a way, in which case we can add it here.

The behavior is (so far) only used for re-throwing an uncaught async error, so
the only thing that happens with the thrown error is that it's printed in the
console, or its string representations are captured by an isolate. This error
object has the same string representation as the original.

The VM version just got better, and that's great. Even if we can't make the JS
version better, it's still an improvement.

+}