Support async/await in the dart2js frontend.

tests/compiler/dart2js/backend_dart/dart_printer_test.dart

 // Copyright (c) 2014, 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.
 
 library dart_printer_test;
 
 import "package:expect/expect.dart";
 import 'package:compiler/implementation/constants/values.dart';
 import 'package:compiler/implementation/dart_backend/backend_ast_nodes.dart';
 import 'package:compiler/implementation/scanner/scannerlib.dart';
@@ skipping 399 matching lines @@
     } else {
       // No optional parameters.
       List<Parameter> required = popList(count-1, <Parameter>[], asParameter);
       required.add(last);
       push(new Parameters(required));
     }
   }
   handleNoFormalParameters(tok) {
     push(new Parameters([]));
   }
-  endUnamedFunction(t) {
+
+  endUnnamedFunction(t) {
     Statement body = pop();
     Parameters parameters = pop();
     push(new FunctionExpression(parameters, body));
   }
+
   handleNoType(Token token) {
     push(null);
   }
 
   endReturnStatement(bool hasExpression, begin, end) {
     // This is also called for functions whose body is "=> expression"
     if (hasExpression) {
       push(new Return(pop()));
     } else {
       push(new Return());
@@ skipping 130 matching lines @@
     ExpressionStatement condition = pop(); // parsed as expression statement
     Expression exp = condition == null ? null : condition.expression;
     Node initializer = pop();
     push(new For(initializer, exp, updates, body));
   }
 
   handleNoExpression(Token token) {
     push(null);
   }
 
-  endForIn(Token begin, Token inKeyword, Token end) {
+  endForIn(Token await, Token begin, Token inKeyword, Token end) {
     Statement body = pop();
     Expression exp = pop();
     Node declaredIdentifier = pop();
     push(new ForIn(declaredIdentifier, exp, body));
   }
 
   handleAssertStatement(Token assertKeyword, Token semicolonToken) {
     Expression exp = pop();
     Expression call = new CallFunction(new Identifier("assert"), [exp]);
     push(new ExpressionStatement(call));
@@ skipping 380 matching lines @@
   checkStatement("do while(x); while (y);");
   checkStatement("{do; while(x); while (y);}");
 
   checkStatement('switch(x) { case 1: case 2: return y; }');
   checkStatement('switch(x) { default: return y; }');
   checkStatement('switch(x) { case 1: x=y; default: return y; }');
   checkStatement('switch(x) { case 1: x=y; y=z; break; default: return y; }');
 
 }