Add List.insert.

sdk/lib/core/list.dart

Index: sdk/lib/core/list.dart
diff --git a/sdk/lib/core/list.dart b/sdk/lib/core/list.dart
index 1e10e864537f3c27883771a26154bcdaf8cec46f..f193c94c8d22859575e2d00872e7a0eeb9071b5c 100644
--- a/sdk/lib/core/list.dart
+++ b/sdk/lib/core/list.dart
@@ -189,7 +189,21 @@ abstract class List<E> implements Collection<E> {
   void clear();
 
   /**
-   * Removes the element at position[index] from the list.
+   * Inserts the element at position [index] in the list.
+   *
+   * This increases the length of the list by one and moves all later elements
+   * up by one position.
+   *
+   * Throws an [ArgumentError] if [index] is not an [int].

[srdjan, 2013/03/04 00:53:47]

That is not correct for checked mode.

[Lasse Reichstein Nielsen, 2013/03/04 09:06:02]

I really prefer to just say "It's an error if ..." and then throw whatever Error
I think fits.
You don't need to know the exact error, and add special code to avoid throwing a
different error.
In this case, requiring a special error in case for something that is already a
bad type is overspecifying. Ofcourse it's an error if the "int" argument is not
assignable to int. No need to say that. You can say that "index" must not be
null.

[floitsch, 2013/03/05 17:51:58]

The documentation had been copied from removeAt.
done.

+   * Throws an [RangeError] if the [index] does not point inside

[srdjan, 2013/03/04 00:53:47]

s/an/a/

+   * the list, or at the position after the last element.
+   * Throws an [UnsupportedError], and doesn't remove the element,

[Lasse Reichstein Nielsen, 2013/03/04 09:06:02]

No need to say that. That's what throwing an UnsupportedError means: I don't
support that operation. We already stated in the List documentation that
fixed-length lists don't support operations that changes the length.

+   * if the length of the list cannot be changed.
+   */
+  void insertAt(int index, E element);
+
+  /**
+   * Removes the element at position [index] from the list.
    *
    * This reduces the length of the list by one and moves all later elements
    * down by one position.