First try at removing ? from HTML.

tools/dom/src/chrome/app_window.dart

Index: tools/dom/src/chrome/app_window.dart
diff --git a/tools/dom/src/chrome/app_window.dart b/tools/dom/src/chrome/app_window.dart
index fdcac46925e747ad7e1a93ca4e414b5eb07116b6..6fb67b61e7dd2e4037485e2449db0481afc55923 100644
--- a/tools/dom/src/chrome/app_window.dart
+++ b/tools/dom/src/chrome/app_window.dart
@@ -15,43 +15,43 @@ 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;
   }
 
@@ -218,13 +218,13 @@ 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;
   }
 
@@ -452,7 +452,7 @@ class API_app_window {
               [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),