Implement 'as' operator.

lib/compiler/implementation/scanner/listener.dart

Index: lib/compiler/implementation/scanner/listener.dart
diff --git a/lib/compiler/implementation/scanner/listener.dart b/lib/compiler/implementation/scanner/listener.dart
index 982540d1bd90149b549e60248ad02a29b49722b9..6c9c41a652bbad603197f2a299f03e75e81de961 100644
--- a/lib/compiler/implementation/scanner/listener.dart
+++ b/lib/compiler/implementation/scanner/listener.dart
@@ -305,6 +305,10 @@ class Listener {
   void endWhileStatement(Token whileKeyword, Token endToken) {
   }
 
+  void handleAsOperator(Token operathor, Token endToken) {
+    // TODO(ahe): Rename [operathor] to "operator" when VM bug is fixed.
+  }
+
   void handleAssignmentExpression(Token token) {
   }
 
@@ -1055,6 +1059,13 @@ class NodeListener extends ElementListener {
     pushNode(new Cascade(popNode()));
   }
 
+  void handleAsOperator(Token operathor, Token endToken) {
+    TypeAnnotation type = popNode();
+    Expression expression = popNode();
+    NodeList arguments = new NodeList.singleton(type);
+    pushNode(new Send(expression, new Operator(operathor), arguments));
+  }
+
   void handleAssignmentExpression(Token token) {
     Node arg = popNode();
     Node node = popNode();