simplify function coercions -- DDC can generate function types in place

lib/src/utils.dart

 // Copyright (c) 2015, 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.
 
 /// Holds a couple utility functions used at various places in the system.
 
 import 'dart:io';
 import 'package:path/path.dart' as path;
 import 'package:analyzer/src/generated/ast.dart'
     show
@@ skipping 456 matching lines @@
   }
 
   void writeAsStringSync(String file, String contents) {
     _ensureParentExists(file);
     new File(file).writeAsStringSync(contents);
   }
 }
 
 DartType getStaticType(Expression e) =>
     e.staticType ?? DynamicTypeImpl.instance;
+
+// TODO(leafp) Factor this out or use an existing library
+class Tuple2<T0, T1> {
+  final T0 e0;
+  final T1 e1;
+  Tuple2(this.e0, this.e1);
+}