Added expand method to iterables.

runtime/lib/growable_array.dart

Index: runtime/lib/growable_array.dart
diff --git a/runtime/lib/growable_array.dart b/runtime/lib/growable_array.dart
index 137a5835208d4afd4dd98a5c021a30061183de39..bb871772de16603b6134fb788f6705e6dd997ca8 100644
--- a/runtime/lib/growable_array.dart
+++ b/runtime/lib/growable_array.dart
@@ -258,6 +258,10 @@ class _GrowableObjectArray<T> implements List<T> {
     return IterableMixinWorkaround.where(this, f);
   }
 
+  Iterable expand(Iterable f(T element)) {
+    return IterableMixinWorkaround.expand(this, f);
+  }
+
   Iterable<T> take(int n) {
     return IterableMixinWorkaround.takeList(this, n);
   }