Made removeAt errors consistent between dart2js and VM.

lib/core/list.dart

Index: lib/core/list.dart
diff --git a/lib/core/list.dart b/lib/core/list.dart
index 436d76024615d908f5853e869f6da552b691e48c..ba113ce36f84e2237c5cfdb283dd3d80ffdf38a5 100644
--- a/lib/core/list.dart
+++ b/lib/core/list.dart
@@ -101,11 +101,11 @@ interface List<E> extends Collection<E> default ListImplementation<E> {
    * This reduces the length of the list by one and moves all later elements
    * down by one position.
    * Returns the removed element.
-   * Throws a [IllegalArgumentException] if [index] is not an integer, and
-   * [IndexOutOfRangeException] if the [index] does not point inside the list.
-   *
-   * Throws a [UnsupportedOperationException] if the list, or the length of
-   * the list, cannot be changed.
+   * Throws an [IllegalArgumentException] if [index] is not an [int].
+   * Throws an [IndexOutOfRangeException] if the [index] does not point inside
+   * the list.
+   * Throws an [UnsupportedOperationException] if the length of the list cannot
+   * be changed.
    */
   E removeAt(int index);
 
@@ -113,7 +113,6 @@ interface List<E> extends Collection<E> default ListImplementation<E> {
    * Pops and returns the last element of the list.
    * Throws a [UnsupportedOperationException] if the length of the
    * list cannot be changed.
-   *
    */
   E removeLast();