Fixing up history test to pass properly on supported platforms.

tools/dom/templates/html/impl/impl_History.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.
 
 part of $LIBRARYNAME;
 
 /// @domName $DOMNAME; @docsEditable true$ANNOTATIONS
 class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
+
+  /**
+   * Checks if the State APIs are supported on the current platform.
+   *
+   * See also:
+   *
+   * * [pushState]
+   * * [replaceState]
+   * * [state]
+   */
+$if DART2JS
+  static bool get supportsState => JS('bool', '!!window.history.pushState');
+$else
+  static bool get supportsState => true;
+$endif
 $!MEMBERS}