Fixes for sunflower

tool/input_sdk/private/js_helper.dart

 // Copyright (c) 2013, 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 _js_helper;
 
 import 'dart:_js_embedded_names' show
     ALL_CLASSES,
     GET_ISOLATE_TAG,
     INTERCEPTED_NAMES,
@@ skipping 564 matching lines @@
 
   static int objectHashCode(object) {
     int hash = JS('int|Null', r'#.$identityHash', object);
     if (hash == null) {
       hash = JS('int', '(Math.random() * 0x3fffffff) | 0');
       JS('void', r'#.$identityHash = #', object, hash);
     }
     return JS('int', '#', hash);
   }
 
-  static _throwFormatException(String string) {
+  static Null _throwFormatException(String string) {

[vsm, 2015/05/26 13:40:58]

This feels a bit strange, but see the casts in the corresponding generated JS
file - both were failing.

[Leaf, 2015/05/26 18:19:45]

This is a bit odd.  I don't understand why Null helps with the casts.  Null
isn't bottom, it's a direct subtype of Object, so I would expect this to be
worse (since it's not even castable to anything except object).

[vsm, 2015/05/27 13:37:21]

Ugh, it turns out that we were reporting an error with Null - we were just
suppressing it and forcing the compile anyway.

OTOH, "void" here currently does work - it's treated as bottom by our rules.  We
could use that.

[Leaf, 2015/05/27 22:16:34]

I don't understand this either... :}  I don't think we treat void as bottom.  We
allow void returning functions to be supertypes of functions which return
anything.  But this is the other way around, isn't it?  We're assigning a String
-> void to a String -> int and String -> double.  This requires that String ->
void be a subtype of String -> int/double, which requires void to be a subtype
of int/double, which it isn't.  This seems like it should still be an error?

     throw new FormatException(string);
   }
 
   static int parseInt(String source,
                       int radix,
                       int handleError(String source)) {
     if (handleError == null) handleError = _throwFormatException;
 
     checkString(source);
     var match = JS('JSExtendableArray|Null',
@@ skipping 2859 matching lines @@
   throw new MainError("No top-level function named 'main'.");
 }
 
 void badMain() {
   throw new MainError("'main' is not a function.");
 }
 
 void mainHasTooManyParameters() {
   throw new MainError("'main' expects too many parameters.");
 }