Issue 21458. Support for 'Add type' Quick Assist in for-each loops.

pkg/analysis_server/test/mock_sdk.dart

Index: pkg/analysis_server/test/mock_sdk.dart
diff --git a/pkg/analysis_server/test/mock_sdk.dart b/pkg/analysis_server/test/mock_sdk.dart
index c87ef8df58f21c903682eaa438b449b8a4b2482d..8673177c23d2e591e4c3fb070357803fe6c19213 100644
--- a/pkg/analysis_server/test/mock_sdk.dart
+++ b/pkg/analysis_server/test/mock_sdk.dart
@@ -60,11 +60,22 @@ class Deprecated extends Object {
 }
 const Object deprecated = const Deprecated("next release");
 
-abstract class List<E> extends Object {
+class Iterator<E> {
+  bool moveNext();
+  E get current;
+}
+
+abstract class Iterable<E> {
+  Iterator<E> get iterator;
+}
+
+abstract class List<E> implements Iterable<E> {
   void add(E value);
   E operator [](int index);
   void operator []=(int index, E value);
+  Iterator<E> get iterator => null;
 }
+
 class Map<K, V> extends Object {}
 
 external bool identical(Object a, Object b);