Add keyLocation to KeyboardEvent constructor for backwards compatibility

sdk/lib/html/dartium/html_dartium.dart

Index: sdk/lib/html/dartium/html_dartium.dart
diff --git a/sdk/lib/html/dartium/html_dartium.dart b/sdk/lib/html/dartium/html_dartium.dart
index fc6b7aaa14683ea8ecd512389c1f0010452becf8..f7c3b61b34766aff837a2645d4ce724b6123d000 100644
--- a/sdk/lib/html/dartium/html_dartium.dart
+++ b/sdk/lib/html/dartium/html_dartium.dart
@@ -24964,7 +24964,8 @@ 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,
@@ -24972,6 +24973,7 @@ class KeyboardEvent extends UIEvent {
     if (view == null) {
       view = window;
     }
+    location ??= keyLocation ?? 1;
     final e = document._createEvent("KeyboardEvent");
     e._initKeyboardEvent(type, canBubble, cancelable, view, "", location,
         ctrlKey, altKey, shiftKey, metaKey);