Nice messages on uncaught exceptions.

dart/sdk/lib/_internal/compiler/implementation/lib/foreign_helper.dart

Index: dart/sdk/lib/_internal/compiler/implementation/lib/foreign_helper.dart
diff --git a/dart/sdk/lib/_internal/compiler/implementation/lib/foreign_helper.dart b/dart/sdk/lib/_internal/compiler/implementation/lib/foreign_helper.dart
index ccc9a4b23f3eede5f8c9c1a2b64aeba86f8c1b4c..c2fd831700ff4cbce344b7efc222bde56cd1d692 100644
--- a/dart/sdk/lib/_internal/compiler/implementation/lib/foreign_helper.dart
+++ b/dart/sdk/lib/_internal/compiler/implementation/lib/foreign_helper.dart
@@ -116,6 +116,20 @@ dynamic JS_CALL_IN_ISOLATE(var isolate, Function function) {}
 dynamic DART_CLOSURE_TO_JS(Function function) {}
 
 /**
+ * Returns a raw reference to the JavaScript function which implements
+ * [function].
+ *
+ * Warning: this is dangerous, you should probably use
+ * [DART_CLOSURE_TO_JS] instead. The returned object is not a valid
+ * Dart closure, does not store the isolate context or arity.
+ *
+ * A valid example of where this can be used is as the second argument
+ * to V8's Error.captureStackTrace. See
+ * https://code.google.com/p/v8/wiki/JavaScriptStackTraceApi.
+ */
+dynamic RAW_DART_FUNCTION_REF(Function function) {}
+
+/**
  * Sets the current isolate to [isolate].
  */
 void JS_SET_CURRENT_ISOLATE(var isolate) {}