Add map to dart:dom collections.

client/dom/frog/dom_frog.dart

Index: client/dom/frog/dom_frog.dart
diff --git a/client/dom/frog/dom_frog.dart b/client/dom/frog/dom_frog.dart
index 0861a876b014c34e86bc08abcf81386a29f62230..fc30d83518d5bef0210ef46a1fc2b25005d14e5a 100644
--- a/client/dom/frog/dom_frog.dart
+++ b/client/dom/frog/dom_frog.dart
@@ -11999,6 +11999,15 @@ class _Collections {
     }
   }
 
+  static List map(Iterable<Object> source,
+                  List<Object> destination,
+                  bool f(o)) {
+    for (final e in source) {
+      destination.add(f(e));
+    }
+    return destination;
+  }
+
   static bool some(Iterable<Object> iterable, bool f(Object o)) {
     for (final e in iterable) {
       if (f(e)) return true;