Make dart2js code retain the original stack trace for uncaught async …

…errors.

R=sigmund@google.com

Review URL: https://codereview.chromium.org/1383213002 .

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

@@ -11,6 +11,7 @@ import 'dart:_js_helper' show
     convertDartClosureToJS,
     getTraceFromException,
     requiresPreamble,
+    wrapException,
     unwrapException;
 import 'dart:_isolate_helper' show
     IsolateNatives,
@@ -518,5 +519,7 @@ class _SyncStarIterable extends IterableBase {
 
 @patch
 void _rethrow(Object error, StackTrace stackTrace) {
-  throw new AsyncError(error, stackTrace);
+  error = wrapException(error);
+  JS("void", "#.stack = #", error, stackTrace.toString());
+  JS("void", "throw #", error);
 }

tests/lib/async/dart2js_uncaught_error_test.dart

@@ -0,0 +1,46 @@
+// Copyright (c) 2013, 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.
+
+import "dart:async";
+import "dart:js";
+import "dart:collection" show Queue;
+import "package:expect/expect.dart";
+import "package:async_helper/async_helper.dart";
+
+var errors = new Queue();
+int ctr = 0;
+
+main() {
+  print("STARTED");
+  asyncStart();
+
+  void errorHandler(self, message, url, line, [column, error]) {
+    print(">> $message / $ctr");
+    var expect = errors.removeFirst();
+    if (ctr == 2) {
+      asyncEnd();
+      print("DONE");
+    }
+    Expect.equals(expect[0].toString(), message);
+    Expect.equals(expect[1].toString(), error["stack"].toString());
+  }
+  context["onerror"] = new JsFunction.withThis(errorHandler);
+
+  void throwit() {
+    var err = ++ctr;
+    try {
+      throw err;
+    } catch (e, s) {
+      errors.add([e, s]);
+      rethrow;
+    }
+  }
+
+  () async {
+    () async {
+      throwit();
+    }();
+    throwit();
+  }();
+}

tests/lib/lib.status

@@ -359,6 +359,9 @@ mirrors/mirrors_used_typedef_declaration_test/01: Crash # Assertion failure: typ
 mirrors/mirrors_used_typedef_declaration_test/none: Crash # Assertion failure: typedef(Foo) has not been checked for cycles.
 mirrors/typedef_library_test: Crash # Assertion failure: typedef(G) has not been checked for cycles.
 
+[ $compiler != dart2js ]
+async/dart2js_uncaught_error_test: Skip  # JS-integration only test
+
 [ $noopt ]
 mirrors/*: SkipByDesign
 convert/chunked_conversion_utf88_test: Pass, Timeout