Make List.from and Iterable.toList default to not growable.

runtime/lib/array.dart

Index: runtime/lib/array.dart
diff --git a/runtime/lib/array.dart b/runtime/lib/array.dart
index 688cfb5e02380e9ee38e4b5c0a10da678da99c7c..a11c59e45363e68bd0aa9a0d70434ec9ebd2cfa9 100644
--- a/runtime/lib/array.dart
+++ b/runtime/lib/array.dart
@@ -228,7 +228,7 @@ class _ObjectArray<E> implements List<E> {
 
   E max([int compare(E a, E b)]) => IterableMixinWorkaround.max(this, compare);
 
-  List<E> toList({ bool growable: false}) {
+  List<E> toList({ bool growable: true}) {
     return new List<E>.from(this, growable: growable);
   }
 
@@ -467,7 +467,7 @@ class _ImmutableArray<E> implements List<E> {
 
   E max([int compare(E a, E b)]) => IterableMixinWorkaround.max(this, compare);
 
-  List<E> toList({ bool growable: false }) {
+  List<E> toList({ bool growable: true }) {
     return new List<E>.from(this, growable: growable);
   }