Make KeyboardEvent cross-browser consistent.

tests/html/keyboard_event_test.dart

+library KeyboardEventTest;
+import '../../pkg/unittest/lib/unittest.dart';
+import '../../pkg/unittest/lib/html_config.dart';
+import 'dart:html';
+
+// Test that we are correctly determining keyCode and charCode uniformly across
+// browsers.
+
+main() {
+
+  useHtmlConfiguration();
+
+  keydownHandlerTest(KeyEvent e) {
+    expect(e.charCode, 0);
+  }
+
+  test('keys', () {
+    // This test currently is pretty much a no-op because we
+    // can't (right now) construct KeyboardEvents with specific keycode/charcode
+    // values (a KeyboardEvent can be "init"-ed but not all the information can
+    // be programmatically populated. It exists as an example for how to use
+    // KeyboardEventController more than anything else.
+    var controller = new KeyboardEventController.keydown(document.window);
+    var func = keydownHandlerTest;
+    controller.add(func);
+    document.window.on.keyDown.add((e) => print('regular listener'), false);
+  });
+}
+
+