Added expand method to iterables.

runtime/lib/byte_array.dart

Index: runtime/lib/byte_array.dart
diff --git a/runtime/lib/byte_array.dart b/runtime/lib/byte_array.dart
index 906259ca147de49689d97d1bae47d58c002a8fa3..14b1b17fb351a3d9b8230bc0f7d49bf7a466d60d 100644
--- a/runtime/lib/byte_array.dart
+++ b/runtime/lib/byte_array.dart
@@ -246,10 +246,14 @@ abstract class _ByteArrayBase {
     return IterableMixinWorkaround.reduce(this, initialValue, combine);
   }
 
-  Collection where(bool f(element)) {
+  Collection where(bool f(int element)) {
     return IterableMixinWorkaround.where(this, f);
   }
 
+  Iterable expand(Iterable f(int element)) {
+    return IterableMixinWorkaround.expand(this, f);
+  }
+
   Iterable<int> take(int n) {
     return IterableMixinWorkaround.takeList(this, n);
   }