Add keyLocation to KeyboardEvent constructor for backwards compatibility

sdk/lib/html/dart2js/html_dart2js.dart

Index: sdk/lib/html/dart2js/html_dart2js.dart
diff --git a/sdk/lib/html/dart2js/html_dart2js.dart b/sdk/lib/html/dart2js/html_dart2js.dart
index 83571d18cdcff9450cbba9db13d408c663464083..8d240427c81fa2b847d98bb74ed4034c512f9e00 100644
--- a/sdk/lib/html/dart2js/html_dart2js.dart
+++ b/sdk/lib/html/dart2js/html_dart2js.dart
@@ -22074,7 +22074,8 @@ class KeyboardEvent extends UIEvent {
       {Window view,
       bool canBubble: true,
       bool cancelable: true,
-      int location: 1,
+      int location,
+      int keyLocation, // Legacy alias for location
       bool ctrlKey: false,
       bool altKey: false,
       bool shiftKey: false,
@@ -22082,6 +22083,7 @@ class KeyboardEvent extends UIEvent {
     if (view == null) {
       view = window;
     }
+    location ??= keyLocation ?? 1;
     KeyboardEvent e = document._createEvent("KeyboardEvent");
     e._initKeyboardEvent(type, canBubble, cancelable, view, "", location,
         ctrlKey, altKey, shiftKey, metaKey);