Add constructors to all the event classes.

client/html/src/KeyboardEventWrappingImplementation.dart

Index: client/html/src/KeyboardEventWrappingImplementation.dart
diff --git a/client/html/src/KeyboardEventWrappingImplementation.dart b/client/html/src/KeyboardEventWrappingImplementation.dart
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+++ b/client/html/src/KeyboardEventWrappingImplementation.dart
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+// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+class KeyboardEventWrappingImplementation extends UIEventWrappingImplementation implements KeyboardEvent {
+  KeyboardEventWrappingImplementation._wrap(ptr) : super._wrap(ptr);
+
+  factory KeyboardEventWrappingImplementation(String type, Window view,
+      String keyIdentifier, int keyLocation, [bool canBubble = true,
+      bool cancelable = true, bool ctrlKey = false, bool altKey = false,
+      bool shiftKey = false, bool metaKey = false, bool altGraphKey = false]) {
+    final e = dom.document.createEvent("KeyboardEvent");
+    e.initKeyboardEvent(type, canBubble, cancelable, LevelDom.unwrap(view),
+        keyIdentifier, keyLocation, ctrlKey, altKey, shiftKey, metaKey,
+        altGraphKey);
+    return LevelDom.wrapKeyboardEvent(e);
+  }
+
+  bool get altGraphKey() => _ptr.altGraphKey;
+
+  bool get altKey() => _ptr.altKey;
+
+  bool get ctrlKey() => _ptr.ctrlKey;
+
+  String get keyIdentifier() => _ptr.keyIdentifier;
+
+  int get keyLocation() => _ptr.keyLocation;
+
+  bool get metaKey() => _ptr.metaKey;
+
+  bool get shiftKey() => _ptr.shiftKey;
+
+  bool getModifierState(String keyIdentifierArg) {
+    return _ptr.getModifierState(keyIdentifierArg);
+  }
+}