fix doc comments in dart:io and collection types

sdk/lib/collection/splay_tree.dart

Index: sdk/lib/collection/splay_tree.dart
diff --git a/sdk/lib/collection/splay_tree.dart b/sdk/lib/collection/splay_tree.dart
index 319b1af59d18a35ae35d4e24d2ff044683f78b9d..a0e6ee39df31397b482aaef79539e591b83ea8da 100644
--- a/sdk/lib/collection/splay_tree.dart
+++ b/sdk/lib/collection/splay_tree.dart
@@ -765,8 +765,8 @@ class SplayTreeSet<E> extends _SplayTree<E, _SplayTreeNode<E>>
   }
 
   // From Set.
-  bool contains(Object object) {
-    return _validKey(object) && _splay(object as dynamic/*=E*/) == 0;
+  bool contains(Object element) {
+    return _validKey(element) && _splay(element as dynamic/*=E*/) == 0;
   }
 
   bool add(E element) {