First try at removing ? from HTML.

sdk/lib/chrome/dart2js/chrome_dart2js.dart

 /// Native wrappers for the Chrome Packaged App APIs.
 ///
 /// These functions allow direct access to the Packaged App APIs, allowing
 /// Chrome Packaged Apps to be written using Dart.
 ///
 /// For more information on these APIs, see the
 /// [Chrome APIs Documentation](http://developer.chrome.com/extensions/api_index.html)
 library chrome;
 
 import 'dart:_foreign_helper' show JS;
@@ skipping 235 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 95 matching lines @@
 
 /**
  * Types
  */
 
 class AppWindowCreateWindowOptions extends ChromeObject {
   /*
    * Public constructor
    */
   AppWindowCreateWindowOptions({String id, int defaultWidth, int defaultHeight, int defaultLeft, int defaultTop, int width, int height, int left, int top, int minWidth, int minHeight, int maxWidth, int maxHeight, String type, String frame, AppWindowBounds bounds, bool transparentBackground, bool hidden, bool singleton}) {
-    if (?id)
+    if (id != null)
       this.id = id;
-    if (?defaultWidth)
+    if (defaultWidth != null)
       this.defaultWidth = defaultWidth;
-    if (?defaultHeight)
+    if (defaultHeight != null)
       this.defaultHeight = defaultHeight;
-    if (?defaultLeft)
+    if (defaultLeft != null)
       this.defaultLeft = defaultLeft;
-    if (?defaultTop)
+    if (defaultTop != null)
       this.defaultTop = defaultTop;
-    if (?width)
+    if (width != null)
       this.width = width;
-    if (?height)
+    if (height != null)
       this.height = height;
-    if (?left)
+    if (left != null)
       this.left = left;
-    if (?top)
+    if (top != null)
       this.top = top;
-    if (?minWidth)
+    if (minWidth != null)
       this.minWidth = minWidth;
-    if (?minHeight)
+    if (minHeight != null)
       this.minHeight = minHeight;
-    if (?maxWidth)
+    if (maxWidth != null)
       this.maxWidth = maxWidth;
-    if (?maxHeight)
+    if (maxHeight != null)
       this.maxHeight = maxHeight;
-    if (?type)
+    if (type != null)
       this.type = type;
-    if (?frame)
+    if (frame != null)
       this.frame = frame;
-    if (?bounds)
+    if (bounds != null)
       this.bounds = bounds;
-    if (?transparentBackground)
+    if (transparentBackground != null)
       this.transparentBackground = transparentBackground;
-    if (?hidden)
+    if (hidden != null)
       this.hidden = hidden;
-    if (?singleton)
+    if (singleton != null)
       this.singleton = singleton;
   }
 
   /*
    * Private constructor
    */
   AppWindowCreateWindowOptions._proxy(_jsObject) : super._proxy(_jsObject);
 
   /*
    * Public accessors
@@ skipping 146 matching lines @@
     JS('void', '#.singleton = #', this._jsObject, singleton);
   }
 
 }
 
 class AppWindowBounds extends ChromeObject {
   /*
    * Public constructor
    */
   AppWindowBounds({int left, int top, int width, int height}) {
-    if (?left)
+    if (left != null)
       this.left = left;
-    if (?top)
+    if (top != null)
       this.top = top;
-    if (?width)
+    if (width != null)
       this.width = width;
-    if (?height)
+    if (height != null)
       this.height = height;
   }
 
   /*
    * Private constructor
    */
   AppWindowBounds._proxy(_jsObject) : super._proxy(_jsObject);
 
   /*
    * Public accessors
@@ skipping 207 matching lines @@
   /// that takes effect.
   // 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.
 
   // TODO(sashab): This override is no longer needed once prefixes are removed.
   void create(String url,
               [AppWindowCreateWindowOptions options,
               void callback(AppWindowAppWindow created_window)]) {
     void __proxy_callback(created_window) {
-      if (?callback)
+      if (callback != null)
         callback(new AppWindowAppWindow._proxy(created_window));
     }
     JS('void', '#.create(#, #, #)', this._jsObject, url, convertArgument(options),
        convertDartClosureToJS(__proxy_callback, 1));
   }
 
   /// Returns an $ref:AppWindow object for the current script context (ie
   /// JavaScript 'window' object). This can also be called on a handle to a
   /// script context for another page, for example:
   /// otherWindow.chrome.app.window.current().
@@ skipping 67 matching lines @@
   /// Callback to be compatible with WebIntents.
   void postFailure() => JS('void', '#.postFailure()', this._jsObject);
 
 }
 
 class AppRuntimeLaunchItem extends ChromeObject {
   /*
    * Public constructor
    */
   AppRuntimeLaunchItem({FileEntry entry, String type}) {
-    if (?entry)
+    if (entry != null)
       this.entry = entry;
-    if (?type)
+    if (type != null)
       this.type = type;
   }
 
   /*
    * Private constructor
    */
   AppRuntimeLaunchItem._proxy(_jsObject) : super._proxy(_jsObject);
 
   /*
    * Public accessors
@@ skipping 12 matching lines @@
     JS('void', '#.type = #', this._jsObject, type);
   }
 
 }
 
 class AppRuntimeLaunchData extends ChromeObject {
   /*
    * Public constructor
    */
   AppRuntimeLaunchData({AppRuntimeIntent intent, String id, List<AppRuntimeLaunchItem> items}) {
-    if (?intent)
+    if (intent != null)
       this.intent = intent;
-    if (?id)
+    if (id != null)
       this.id = id;
-    if (?items)
+    if (items != null)
       this.items = items;
   }
 
   /*
    * Private constructor
    */
   AppRuntimeLaunchData._proxy(_jsObject) : super._proxy(_jsObject);
 
   /*
    * Public accessors
@@ skipping 23 matching lines @@
     JS('void', '#.items = #', this._jsObject, convertArgument(items));
   }
 
 }
 
 class AppRuntimeIntentResponse extends ChromeObject {
   /*
    * Public constructor
    */
   AppRuntimeIntentResponse({int intentId, bool success, Object data}) {
-    if (?intentId)
+    if (intentId != null)
       this.intentId = intentId;
-    if (?success)
+    if (success != null)
       this.success = success;
-    if (?data)
+    if (data != null)
       this.data = data;
   }
 
   /*
    * Private constructor
    */
   AppRuntimeIntentResponse._proxy(_jsObject) : super._proxy(_jsObject);
 
   /*
    * Public accessors
@@ skipping 23 matching lines @@
 
 /**
  * Events
  */
 
 /// Fired when an app is launched from the launcher or in response to a web
 /// intent.
 class Event_app_runtime_onLaunched extends Event {
   void addListener(void callback(AppRuntimeLaunchData launchData)) {
     void __proxy_callback(launchData) {
-      if (?callback) {
+      if (callback != null) {
         callback(new AppRuntimeLaunchData._proxy(launchData));
       }
     }
     super.addListener(callback);
   }
 
   void removeListener(void callback(AppRuntimeLaunchData launchData)) {
     void __proxy_callback(launchData) {
-      if (?callback) {
+      if (callback != null) {
         callback(new AppRuntimeLaunchData._proxy(launchData));
       }
     }
     super.removeListener(callback);
   }
 
   bool hasListener(void callback(AppRuntimeLaunchData launchData)) {
     void __proxy_callback(launchData) {
-      if (?callback) {
+      if (callback != null) {
         callback(new AppRuntimeLaunchData._proxy(launchData));
       }
     }
     super.hasListener(callback);
   }
 
   Event_app_runtime_onLaunched(jsObject) : super._(jsObject, 1);
 }
 
 /// Fired at Chrome startup to apps that were running when Chrome last shut
@@ skipping 30 matching lines @@
   /// postIntentResponse is an internal method to responds to an intent
   /// previously sent to a packaged app. This is identified by intentId, and
   /// should only be invoked at most once per intentId.
   void postIntentResponse(AppRuntimeIntentResponse intentResponse) => JS('void', '#.postIntentResponse(#)', this._jsObject, convertArgument(intentResponse));
 
   API_app_runtime(this._jsObject) {
     onLaunched = new Event_app_runtime_onLaunched(JS('', '#.onLaunched', this._jsObject));
     onRestarted = new Event_app_runtime_onRestarted(JS('', '#.onRestarted', this._jsObject));
   }
 }