dart2js: add comments.

pkg/compiler/lib/src/js_emitter/code_emitter_task.dart

Index: pkg/compiler/lib/src/js_emitter/code_emitter_task.dart
diff --git a/pkg/compiler/lib/src/js_emitter/code_emitter_task.dart b/pkg/compiler/lib/src/js_emitter/code_emitter_task.dart
index de0592bf213c3ee21daf25628e90cbb644ad198d..317d6bd418d046f1ce8fbc3896ae42ef6d404d09 100644
--- a/pkg/compiler/lib/src/js_emitter/code_emitter_task.dart
+++ b/pkg/compiler/lib/src/js_emitter/code_emitter_task.dart
@@ -249,6 +249,9 @@ class CodeEmitterTask extends CompilerTask {
     // to identify them later and make sure we only emit "empty shells" without
     // fields, etc.
     typeTestEmitter.computeRtiNeededClasses();
+
+    // TODO(floitsch): either change the name, or get the rti-classes
+    // differently.
     typeTestEmitter.rtiNeededClasses.removeAll(neededClasses);
     // rtiNeededClasses now contains only the "empty shells".
     neededClasses.addAll(typeTestEmitter.rtiNeededClasses);