Revert "Remove deprecated mappedBy."

sdk/lib/collection/collections.dart

Index: sdk/lib/collection/collections.dart
diff --git a/sdk/lib/collection/collections.dart b/sdk/lib/collection/collections.dart
index fc27c9158e9ff44236737fdcf145722a37a1ad4d..06aa7677c73b96bd51a0f7e5d5a770ccd6e690a2 100644
--- a/sdk/lib/collection/collections.dart
+++ b/sdk/lib/collection/collections.dart
@@ -321,6 +321,11 @@ class IterableMixinWorkaround {
     return new MappedListIterable(list, f);
   }
 
+  static List mappedByList(List list, f(var element)) {
+    // This is currently a List as well as an Iterable.
+    return new MappedList(list, f);
+  }
+
   static Iterable expand(Iterable iterable, Iterable f(var element)) {
     return new ExpandIterable(iterable, f);
   }
@@ -469,6 +474,11 @@ class Collections {
 
   /** Deprecated. Use the same method in [IterableMixinWorkaround] instead.*/
   @deprecated
+  static List mappedByList(List list, f(var element))
+      => IterableMixinWorkaround.mappedByList(list, f);
+
+  /** Deprecated. Use the same method in [IterableMixinWorkaround] instead.*/
+  @deprecated
   static Iterable takeList(List list, int n)
       => IterableMixinWorkaround.takeList(list, n);