Make static tear-off closures a class, like instance tear-off closures.

sdk/lib/_internal/compiler/implementation/lib/js_helper.dart

 // Copyright (c) 2012, 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:collection';
 import 'dart:_foreign_helper' show DART_CLOSURE_TO_JS,
                                    JS,
                                    JS_CALL_IN_ISOLATE,
@@ skipping 1076 matching lines @@
   if (value is bool) return value;
   throw new TypeErrorImplementation(value, 'bool');
 }
 
 boolTypeCast(value) {
   if (value is bool || value == null) return value;
   throw new CastErrorImplementation(
       Primitives.objectTypeName(value), 'bool');
 }
 
-functionTypeCheck(value) {
-  if (value == null) return value;
-  if (value is Function) return value;
-  throw new TypeErrorImplementation(value, 'Function');
-}
-
-functionTypeCast(value) {
-  if (value is Function || value == null) return value;
-  throw new CastErrorImplementation(
-      Primitives.objectTypeName(value), 'Function');
-}
-
 intTypeCheck(value) {
   if (value == null) return value;
   if (value is int) return value;
   throw new TypeErrorImplementation(value, 'int');
 }
 
 intTypeCast(value) {
   if (value is int || value == null) return value;
   throw new CastErrorImplementation(
       Primitives.objectTypeName(value), 'int');
@@ skipping 266 matching lines @@
                               expectedArgumentNames);
 }
 
 /**
  * Called by generated code when a static field's initializer references the
  * field that is currently being initialized.
  */
 void throwCyclicInit(String staticName) {
   throw new RuntimeError("Cyclic initialization for static $staticName");
 }