Add Null class to dart:core.

runtime/vm/class_finalizer.cc

 // 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.
 
 #include "vm/class_finalizer.h"
 
 #include "vm/flags.h"
 #include "vm/heap.h"
 #include "vm/isolate.h"
 #include "vm/longjump.h"
@@ skipping 1885 matching lines @@
                 String::Handle(cls.Name()).ToCString(),
                 String::Handle(super_type.UserVisibleName()).ToCString());
   }
 
   // If cls belongs to core lib or to core lib's implementation, restrictions
   // about allowed interfaces are lifted.
   if (!cls_belongs_to_core_lib) {
     // Prevent extending core implementation classes.
     bool is_error = false;
     switch (interface_class.id()) {
+      case kNullCid:
       case kNumberCid:
       case kIntegerCid:  // Class Integer, not int.
       case kSmiCid:
       case kMintCid:
       case kBigintCid:
       case kDoubleCid:  // Class Double, not double.
       case kOneByteStringCid:
       case kTwoByteStringCid:
       case kExternalOneByteStringCid:
       case kExternalTwoByteStringCid:
@@ skipping 49 matching lines @@
     }
     interface_class = interface.type_class();
     if (interface_class.IsSignatureClass()) {
       const Script& script = Script::Handle(cls.script());
       ReportError(Error::Handle(),  // No previous error.
                   script, cls.token_pos(),
                   "function type alias '%s' may not be used as interface",
                   String::Handle(interface_class.Name()).ToCString());
     }
     // Verify that unless cls belongs to core lib, it cannot extend or implement
-    // any of bool, num, int, double, String, Function, dynamic.
+    // any of Null, bool, num, int, double, String, Function, dynamic.
     // The exception is signature classes, which are compiler generated and
     // represent a function type, therefore implementing the Function interface.
     if (!cls_belongs_to_core_lib) {
-      if (interface.IsBoolType() ||
+      if (interface.IsNullType() ||
+          interface.IsBoolType() ||
           interface.IsNumberType() ||
           interface.IsIntType() ||
           interface.IsDoubleType() ||
           interface.IsStringType() ||
           interface.IsDynamicType()) {
         const Script& script = Script::Handle(cls.script());
         ReportError(Error::Handle(),  // No previous error.
                     script, cls.token_pos(),
                     "'%s' is not allowed to extend or implement '%s'",
                     String::Handle(cls.Name()).ToCString(),
@@ skipping 229 matching lines @@
   expected_name ^= String::New("_offset");
   ASSERT(String::EqualsIgnoringPrivateKey(name, expected_name));
   field ^= fields_array.At(2);
   ASSERT(field.Offset() == TypedDataView::length_offset());
   name ^= field.name();
   ASSERT(name.Equals("length"));
 #endif
 }
 
 }  // namespace dart