Add "growable" parameter to List.filled constructor.

sdk/lib/_internal/js_runtime/lib/core_patch.dart

Index: sdk/lib/_internal/js_runtime/lib/core_patch.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/core_patch.dart b/sdk/lib/_internal/js_runtime/lib/core_patch.dart
index d55524211342d233eaaec77493a5b3ad8833a037..301517ee669f5a532008375f12048c4f37bc0ba0 100644
--- a/sdk/lib/_internal/js_runtime/lib/core_patch.dart
+++ b/sdk/lib/_internal/js_runtime/lib/core_patch.dart
@@ -281,8 +281,9 @@ class List<E> {
   }
 
   @patch
-  factory List.filled(int length, E fill) {
-    List result = new JSArray<E>.fixed(length);
+  factory List.filled(int length, E fill, {bool growable: false}) {
+    List result = growable ? new JSArray<E>.growable(length)
+                           : new JSArray<E>.fixed(length);
     if (length != 0 && fill != null) {
       for (int i = 0; i < result.length; i++) {
         result[i] = fill;