Third round of cleanups for new optional parameter semantics.

lib/html/dartium/html_dartium.dart

Index: lib/html/dartium/html_dartium.dart
===================================================================
--- lib/html/dartium/html_dartium.dart	(revision 13762)
+++ lib/html/dartium/html_dartium.dart	(working copy)
@@ -22626,10 +22626,10 @@
 abstract class MouseEvent implements UIEvent {
 
   factory MouseEvent(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]) =>
+      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}) =>
       _MouseEventFactoryProvider.createMouseEvent(
           type, view, detail, screenX, screenY,
           clientX, clientY, button, canBubble, cancelable,
@@ -43018,9 +43018,9 @@
 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,