Add List.insert.

sdk/lib/_collection_dev/list.dart

Index: sdk/lib/_collection_dev/list.dart
diff --git a/sdk/lib/_collection_dev/list.dart b/sdk/lib/_collection_dev/list.dart
index 9384627d9b97c62565b3dca4adfc9ab6ec1b8f95..9989a2d9265fe4f044c864660aa1e9861e465359 100644
--- a/sdk/lib/_collection_dev/list.dart
+++ b/sdk/lib/_collection_dev/list.dart
@@ -61,6 +61,11 @@ abstract class FixedLengthListBase<E> extends ListBase<E> {
         "Cannot add to a fixed-length list");
   }
 
+  void insertAt(int index, E value) {
+    throw new UnsupportedError(
+        "Cannot add to a fixed-length list");
+  }
+
   void addAll(Iterable<E> iterable) {
     throw new UnsupportedError(
         "Cannot add to a fixed-length list");
@@ -137,6 +142,11 @@ abstract class UnmodifiableListBase<E> extends ListBase<E> {
         "Cannot add to an unmodifiable list");
   }
 
+  E insertAt(int index, E value) {
+    throw new UnsupportedError(
+        "Cannot add to an unmodifiable list");
+  }
+
   void addAll(Iterable<E> iterable) {
     throw new UnsupportedError(
         "Cannot add to an unmodifiable list");