Fix problem introduced with 043c0096adeec45c0b7c544ce717956e1dd9942b.

sdk/lib/js/dart2js/js_dart2js.dart

Index: sdk/lib/js/dart2js/js_dart2js.dart
diff --git a/sdk/lib/js/dart2js/js_dart2js.dart b/sdk/lib/js/dart2js/js_dart2js.dart
index abe5139ccd1115f3a5a0b758ac065a7fd74bf949..d97523be3a3d4a65b313fe46273ef2bcee7407b4 100644
--- a/sdk/lib/js/dart2js/js_dart2js.dart
+++ b/sdk/lib/js/dart2js/js_dart2js.dart
@@ -499,8 +499,8 @@ class JsArray<E> extends JsObject with ListMixin<E> {
   }
 
   void setRange(int start, int end, Iterable<E> iterable, [int skipCount = 0]) {
-    _checkRange(start, end, length);
-    length = end - start;
+    _checkRange(start, end, this.length);
+    int length = end - start;
     if (length == 0) return;
     if (skipCount < 0) throw new ArgumentError(skipCount);
     var args = [start, length]..addAll(iterable.skip(skipCount).take(length));