Fix all for-in warnings in dart2js

pkg/compiler/lib/src/tree/nodes.dart

Index: pkg/compiler/lib/src/tree/nodes.dart
diff --git a/pkg/compiler/lib/src/tree/nodes.dart b/pkg/compiler/lib/src/tree/nodes.dart
index 6eb072163acb07219144fc405b3fa72b20607d95..8b9234df38d987bdd904b55b2adec7d07e87bb5e 100644
--- a/pkg/compiler/lib/src/tree/nodes.dart
+++ b/pkg/compiler/lib/src/tree/nodes.dart
@@ -572,7 +572,7 @@ class NewExpression extends Expression {
   Token getEndToken() => send.getEndToken();
 }
 
-class NodeList extends Node {
+class NodeList extends Node with IterableMixin<Node> {
   final Link<Node> nodes;
   final Token beginToken;
   final Token endToken;
@@ -588,6 +588,13 @@ class NodeList extends Node {
 
   NodeList asNodeList() => this;
 
+  // Override [IterableMixin.toString] with same code as [Node.toString].
+  toString() => unparse(this);
+
+  get length {
+    throw new UnsupportedError('use slowLength() instead of get:length');
+  }
+
   int slowLength() {
     int result = 0;
     for (Link<Node> cursor = nodes; !cursor.isEmpty; cursor = cursor.tail) {