First try at removing ? from HTML.

tools/dom/src/chrome/utils.dart

 // Copyright (c) 2013, 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.
 
 /**
  * A set of utilities for use with the Chrome Extension APIs.
  *
  * Allows for easy access to required JS objects.
  */
 part of chrome;
@@ skipping 209 matching lines @@
   /// Registers rules to handle events.
   ///
   /// [eventName] is the name of the event this function affects and [rules] are
   /// the rules to be registered. These do not replace previously registered
   /// rules. [callback] is called with registered rules.
   ///
   void addRules(String eventName, List<Rule> rules,
                 [void callback(List<Rule> rules)]) {
     // proxy the callback
     void __proxy_callback(List rules) {
-      if (?callback) {
+      if (callback != null) {
         List<Rule> __proxy_rules = new List<Rule>();
 
         for (Object o in rules)
           __proxy_rules.add(new Rule._proxy(o));
 
         callback(__proxy_rules);
       }
     }
 
     JS('void',
        '#.addRules(#, #, #)',
        this._jsObject,
        convertArgument(eventName),
        convertArgument(rules),
        convertDartClosureToJS(__proxy_callback, 1)
     );
   }
 
   /// Returns currently registered rules.
   ///
   /// [eventName] is the name of the event this function affects and, if an array
   /// is passed as [ruleIdentifiers], only rules with identifiers contained in
   /// this array are returned. [callback] is called with registered rules.
   ///
   void getRules(String eventName, [List<String> ruleIdentifiers,
                                    void callback(List<Rule> rules)]) {
     // proxy the callback
     void __proxy_callback(List rules) {
-      if (?callback) {
+      if (callback != null) {
         List<Rule> __proxy_rules = new List<Rule>();
 
         for (Object o in rules)
           __proxy_rules.add(new Rule._proxy(o));
 
         callback(__proxy_rules);
       }
     }
 
     JS('void',
@@ skipping 16 matching lines @@
                                       void callback()]) =>
       JS('void',
          '#.removeRules(#, #, #)',
          this._jsObject,
          convertArgument(eventName),
          convertArgument(ruleIdentifiers),
          convertDartClosureToJS(callback, 0)
       );
 }