First try at removing ? from HTML.

sdk/lib/web_audio/dart2js/web_audio_dart2js.dart

 library dart.dom.web_audio;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:_collection-dev';
 import 'dart:html';
 import 'dart:html_common';
 import 'dart:typed_data';
 import 'dart:_js_helper' show Creates, Returns, convertDartClosureToJS;
 import 'dart:_foreign_helper' show JS;
@@ skipping 93 matching lines @@
 // BSD-style license that can be found in the LICENSE file.
 
 
 @DomName('AudioBufferSourceNode')
 class AudioBufferSourceNode extends AudioSourceNode native "AudioBufferSourceNode" {
 
   // TODO(efortuna): Remove these methods when Chrome stable also uses start
   // instead of noteOn.
   void start(num when, [num grainOffset, num grainDuration]) {
     if (JS('bool', '!!#.start', this)) {
-      if (?grainDuration) {
+      if (grainOffset != null) {
+        JS('void', '#.start(#, #)', this, when, grainOffset);
+      } else if (grainDuration != null) {
         JS('void', '#.start(#, #, #)', this, when, grainOffset, grainDuration);
-      } else if (?grainOffset) {
-        JS('void', '#.start(#, #)', this, when, grainOffset);
       } else {
         JS('void', '#.start(#)', this, when);
       }
     } else {
-      if (?grainDuration) {
+      if (grainOffset != null) {
+        JS('void', '#.noteOn(#, #)', this, when, grainOffset);
+      } else if (grainDuration != null) {
         JS('void', '#.noteOn(#, #, #)', this, when, grainOffset, grainDuration);
-      } else if (?grainOffset) {
-        JS('void', '#.noteOn(#, #)', this, when, grainOffset);
       } else {
         JS('void', '#.noteOn(#)', this, when);
       }
     }
   }
 
   void stop(num when) {
     if (JS('bool', '!!#.stop', this)) {
       JS('void', '#.stop(#)', this, when);
     } else {
@@ skipping 157 matching lines @@
       return JS('GainNode', '#.createGain()', this);
     } else {
       return JS('GainNode', '#.createGainNode()', this);
     }
   }
 
   ScriptProcessorNode createScriptProcessor(int bufferSize,
       [int numberOfInputChannels, int numberOfOutputChannels]) {
     var function = JS('dynamic', '#.createScriptProcessor || '
         '#.createJavaScriptNode', this, this);
-    if (?numberOfOutputChannels) {
+    if (numberOfInputChannels != null) {
+      return JS('ScriptProcessorNode', '#.call(#, #, #)', function, this,
+          bufferSize, numberOfInputChannels);
+    } else if (numberOfOutputChannels != null) {
       return JS('ScriptProcessorNode', '#.call(#, #, #, #)', function, this,
           bufferSize, numberOfInputChannels, numberOfOutputChannels);
-    } else if (?numberOfInputChannels) {
-      return JS('ScriptProcessorNode', '#.call(#, #, #)', function, this,
-          bufferSize, numberOfInputChannels);
     } else {
       return JS('ScriptProcessorNode', '#.call(#, #)', function, this,
           bufferSize);
     }
   }
 }
 // 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.
 
@@ skipping 552 matching lines @@
 }
 // 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.
 
 
 @DocsEditable
 @DomName('WaveTable')
 class WaveTable native "WaveTable" {
 }