Add a method on native classes for is checks. Reduces the code for generating is checks.

frog/leg/native_handler.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('native');
 #import('../../lib/uri/uri.dart');
 #import('leg.dart');
 #import('elements/elements.dart');
 #import('scanner/scannerlib.dart');
 #import('ssa/ssa.dart');
@@ skipping 41 matching lines @@
         addSubtypes(classElement, emitter);
       }
     }
   }
   if (hasNativeClass) {
     compiler.registerStaticUse(compiler.findHelper(
         const SourceString('dynamicFunction')));
     compiler.registerStaticUse(compiler.findHelper(
         const SourceString('dynamicSetMetadata')));
     compiler.registerStaticUse(compiler.findHelper(
-        const SourceString('dynamicIsCheck')));
+        const SourceString('defineProperty')));
   }
 }
 
 void maybeEnableNative(Compiler compiler,
                        LibraryElement library,
                        Uri uri) {
   String libraryName = uri.toString();
   if (library.script.name.contains('dart/frog/tests/native/src')
       || libraryName == 'dart:dom'
       || libraryName == 'dart:isolate'
@@ skipping 267 matching lines @@
             const LiteralDartString('void'),
             <HInstruction>[jsClosure]));
       }
     });
     LiteralString jsCode = node.arguments.head;
     builder.push(new HForeign(jsCode.dartString,
                               const LiteralDartString('Object'),
                               <HInstruction>[]));
   }
 }