Merge request - fixes dart2js async problems.

pkg/compiler/lib/src/dart_types.dart

Index: pkg/compiler/lib/src/dart_types.dart
===================================================================
--- pkg/compiler/lib/src/dart_types.dart	(revision 43839)
+++ pkg/compiler/lib/src/dart_types.dart	(working copy)
@@ -475,7 +475,7 @@
    * Returns the type as an instance of class [other], if possible, null
    * otherwise.
    */
-  DartType asInstanceOf(ClassElement other) {
+  InterfaceType asInstanceOf(ClassElement other) {
     other = other.declaration;
     if (element == other) return this;
     InterfaceType supertype = element.asInstanceOf(other);