Remove JS_CONST from CssStyleDeclaration, causes DDC problems

tools/dom/templates/html/dart2js/html_dart2js.darttemplate

 // 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.
 
 // DO NOT EDIT - unless you are editing documentation as per:
 // https://code.google.com/p/dart/wiki/ContributingHTMLDocumentation
 // Auto-generated dart:html library.
 
 /**
  * HTML elements and other resources for web-based applications that need to
@@ skipping 44 matching lines @@
     JSName, Native, Returns, ForceInline,
     findDispatchTagForInterceptorClass, setNativeSubclassDispatchRecord,
     makeLeafDispatchRecord;
 import 'dart:_interceptors' show
     Interceptor, JSExtendableArray, JSUInt31,
     findInterceptorConstructorForType,
     findConstructorForNativeSubclassType,
     getNativeInterceptor,
     setDispatchProperty;
 import 'dart:_isolate_helper' show IsolateNatives;
-import 'dart:_foreign_helper' show JS, JS_INTERCEPTOR_CONSTANT, JS_CONST;
+import 'dart:_foreign_helper' show JS, JS_INTERCEPTOR_CONSTANT;
 
 export 'dart:math' show Rectangle, Point;
 
 $!GENERATED_DART_FILES
 
 part '$AUXILIARY_DIR/AttributeMap.dart';
 part '$AUXILIARY_DIR/CanvasImageSource.dart';
 part '$AUXILIARY_DIR/CrossFrameTypes.dart';
 part '$AUXILIARY_DIR/CssClassSet.dart';
 part '$AUXILIARY_DIR/CssRectangle.dart';
@@ skipping 72 matching lines @@
 createCustomUpgrader(Type customElementClass, $this) => $this;
 
 /**
  * Emitted for any setlike IDL entry needs a callback signature.
  * Today there is only one.
  */
 @DomName('FontFaceSetForEachCallback')
 @Experimental() // untriaged
 typedef void FontFaceSetForEachCallback(
     FontFace fontFace, FontFace fontFaceAgain, FontFaceSet set);
-