First try at removing ? from HTML.

tools/dom/templates/html/dart2js/impl_AudioBufferSourceNode.darttemplate

Index: tools/dom/templates/html/dart2js/impl_AudioBufferSourceNode.darttemplate
diff --git a/tools/dom/templates/html/dart2js/impl_AudioBufferSourceNode.darttemplate b/tools/dom/templates/html/dart2js/impl_AudioBufferSourceNode.darttemplate
index 36529bba49d15b5ac2a2f4c6ed2437a4aec213ab..4ea48782d4fc3d61f237bc8eabf2fc3ed1cf9aba 100644
--- a/tools/dom/templates/html/dart2js/impl_AudioBufferSourceNode.darttemplate
+++ b/tools/dom/templates/html/dart2js/impl_AudioBufferSourceNode.darttemplate
@@ -10,17 +10,17 @@ $(ANNOTATIONS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
   // instead of noteOn.
   void start(num when, [num grainOffset, num grainDuration]) {
     if (JS('bool', '!!#.start', this)) {
-      if (?grainDuration) {
+      if (grainDuration != null) {
         JS('void', '#.start(#, #, #)', this, when, grainOffset, grainDuration);
-      } else if (?grainOffset) {
+      } else if (grainOffset != null) {
         JS('void', '#.start(#, #)', this, when, grainOffset);
       } else {
         JS('void', '#.start(#)', this, when);
       }
     } else {
-      if (?grainDuration) {
+      if (grainDuration != null) {
         JS('void', '#.noteOn(#, #, #)', this, when, grainOffset, grainDuration);
-      } else if (?grainOffset) {
+      } else if (grainOffset != null) {
         JS('void', '#.noteOn(#, #)', this, when, grainOffset);
       } else {
         JS('void', '#.noteOn(#)', this, when);