Add optional arguments to our indexOf/lastIndexOf methods.

corelib/src/list.dart

Index: corelib/src/list.dart
===================================================================
--- corelib/src/list.dart	(revision 942)
+++ corelib/src/list.dart	(working copy)
@@ -79,14 +79,14 @@
    * list from index [startIndex] to the length of the list. Returns
    * -1 if [element] is not found.
    */
-  int indexOf(E element, int startIndex);
+  int indexOf(E element, [int startIndex]);
 
   /**
    * Returns the last index of [element] in this list. Searches this
-   * list from index [startIndex] to 0. Returns -1 if [element] is
-   * not found.
+   * list from index [fromIndex] (inclusive) to 0. Returns -1 if
+   * [element] is not found.
    */
-  int lastIndexOf(E element, int startIndex);
+  int lastIndexOf(E element, [int fromIndex]);
 
   /**
    * Removes all elements in the list. The length of the list