[GObject] Wrap KeyboardEvent
https://bugs.webkit.org/show_bug.cgi?id=119651

Reviewed by Christophe Dumez.

This exposes KeyboardEvent to our GObject API. It is required for handling
keyboard events, such as keydown, keypress, and so on.

* bindings/gobject/GNUmakefile.am:
* bindings/gobject/WebKitDOMPrivate.cpp:
(WebKit::wrap): make sure we create a WebKitDOMKeyboardEvent for a DOM event that
is a KeyboardEvent.
* bindings/scripts/CodeGeneratorGObject.pm:
(GetBaseClass): make WebKitDOMEvent be WebKitDOMKeyboardEvent's parent, like we do
for WebKitDOMMouseEvent.
* dom/KeyboardEvent.idl: generate a single initialization method.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@153921 268f45cc-cd09-0410-ab3c-d52691b4dbfc