Enforce rule in vm that factory name must match enclosing class name.

runtime/lib/error.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.
 // Errors are created and thrown by DartVM only.
 // Changes here should also be reflected in corelib/error.dart as well
 
 class AssertionErrorImplementation implements AssertionError {
   factory AssertionErrorImplementation._uninstantiable() {
     throw new UnsupportedError(
         "AssertionError can only be allocated by the VM");
@@ skipping 35 matching lines @@
   }
   final String srcType;
   final String dstType;
   final String dstName;
   final String malformedError;
 }
 
 class CastErrorImplementation
     extends TypeErrorImplementation
     implements CastError {
-  factory CastError._uninstantiable() {
+  factory CastErrorImplementation._uninstantiable() {
     throw new UnsupportedError(
         "CastError can only be allocated by the VM");
   }
   // A CastError is allocated by TypeError._throwNew() when dst_name equals
   // Exceptions::kCastErrorDstName.
   String toString() {
     String str = (malformedError != null) ? malformedError : "";
     if ((dstName != null) && (dstName.length > 0)) {
       str = "${str}type '$srcType' is not a subtype of "
             "type '$dstType' in type cast.";
@@ skipping 58 matching lines @@
 
   String toString() {
     return "Cannot instantiate abstract class $className: "
            "url '$url' line $line";
   }
 
   final String className;
   final String url;
   final int line;
 }