Third round of cleanups for new optional parameter semantics.

lib/html/src/shared_FactoryProviders.dart

Index: lib/html/src/shared_FactoryProviders.dart
===================================================================
--- lib/html/src/shared_FactoryProviders.dart	(revision 13762)
+++ lib/html/src/shared_FactoryProviders.dart	(working copy)
@@ -23,9 +23,9 @@
 class _MouseEventFactoryProvider {
   static MouseEvent createMouseEvent(String type, Window view, int detail,
       int screenX, int screenY, int clientX, int clientY, int button,
-      [bool canBubble = true, bool cancelable = true, bool ctrlKey = false,
-      bool altKey = false, bool shiftKey = false, bool metaKey = false,
-      EventTarget relatedTarget = null]) {
+      bool canBubble, bool cancelable, bool ctrlKey,
+      bool altKey, bool shiftKey, bool metaKey,
+      EventTarget relatedTarget) {
     final e = _document.$dom_createEvent("MouseEvent");
     e.$dom_initMouseEvent(type, canBubble, cancelable, view, detail,
         screenX, screenY, clientX, clientY, ctrlKey, altKey, shiftKey, metaKey,