cps2js: Clean up some obsolete TODOs.

pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart

Index: pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart
diff --git a/pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart b/pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart
index d1f51fcadabcd01738f0f0f8957c1e78c8f09fc7..f1d56163157da376b22d540653a20edb6d686c7e 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart
@@ -454,7 +454,8 @@ class SetMutableVariable extends Expression implements InteriorNode {
 ///
 ///   let rec [variable] = [definition] in [body]
 ///
-class DeclareFunction extends Expression implements InteriorNode {
+class DeclareFunction extends Expression
+                      implements InteriorNode, DartSpecificNode {
   final MutableVariable variable;
   final FunctionDefinition definition;
   Expression body;
@@ -528,9 +529,12 @@ class Branch extends Expression {
 
 /// Marker interface for nodes that are only handled in the JavaScript backend.
 ///
-/// These nodes are generated by the unsugar step and need special translation
-/// to the Tree IR, which is implemented in JsTreeBuilder.
-abstract class JsSpecificNode {}
+/// These nodes are generated by the unsugar step or the [JsIrBuilder] and need
+/// special translation to the Tree IR, which is implemented in JsTreeBuilder.
+abstract class JsSpecificNode implements Node {}
+
+/// Marker interface for nodes that are only handled inthe Dart backend.
+abstract class DartSpecificNode implements Node {}
 
 /// Directly assigns to a field on a given object.
 class SetField extends Expression implements InteriorNode, JsSpecificNode {
@@ -656,7 +660,7 @@ class LiteralMap extends Primitive {
 }
 
 /// Create a non-recursive function.
-class CreateFunction extends Primitive {
+class CreateFunction extends Primitive implements DartSpecificNode {
   final FunctionDefinition definition;
 
   CreateFunction(this.definition);
@@ -795,7 +799,7 @@ class FunctionDefinition extends Node
   bool get isAbstract => body == null;
 }
 
-abstract class Initializer extends Node {}
+abstract class Initializer extends Node implements DartSpecificNode {}
 
 class FieldInitializer extends Initializer {
   final FieldElement element;