Fix checked mode on browser.

lib/compiler/implementation/js_backend/native_emitter.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.
 
 class NativeEmitter {
 
   CodeEmitterTask emitter;
   CodeBuffer nativeBuffer;
 
   // Classes that participate in dynamic dispatch. These are the
@@ skipping 132 matching lines @@
     assert(classElement.backendMembers.isEmpty());
     String quotedName = classElement.nativeName.slowToString();
     if (isNativeLiteral(quotedName)) {
       generateNativeLiteral(classElement);
       // The native literal kind needs to be dealt with specially when
       // generating code for it.
       return;
     }
 
     CodeBuffer fieldBuffer = new CodeBuffer();
-    emitter.emitClassFields(classElement, fieldBuffer);
+    List<String> checkedSetters =
+        emitter.emitClassFields(classElement, fieldBuffer);
 
     CodeBuffer methodBuffer = new CodeBuffer();
     emitter.emitInstanceMembers(classElement, methodBuffer, false);
 
     if (methodBuffer.isEmpty() && fieldBuffer.isEmpty()) return;
 
     String nativeName = toNativeName(classElement);
     nativeBuffer.add("$defineNativeClassName('$nativeName', [");
     nativeBuffer.add(fieldBuffer);
     nativeBuffer.add('], {');
+    if (!checkedSetters.isEmpty()) {
+      nativeBuffer.add('${Strings.join(checkedSetters, ",\n")}');
+      nativeBuffer.add(',\n');
+    }
     nativeBuffer.add(methodBuffer);
     nativeBuffer.add('\n});\n\n');
 
     classesWithDynamicDispatch.add(classElement);
   }
 
   List<ClassElement> getDirectSubclasses(ClassElement cls) {
     List<ClassElement> result = directSubtypes[cls];
     return result === null ? const<ClassElement>[] : result;
   }
@@ skipping 258 matching lines @@
         if (!first) targetBuffer.add(",\n");
         targetBuffer.add(" $name: $function");
         first = false;
       });
       targetBuffer.add("\n});\n\n");
     }
     targetBuffer.add('$nativeBuffer');
     targetBuffer.add('\n');
   }
 }