Allow DDHotKey integration into code which includes WebKit in precompiled header

[nbeadman]

Fixed compiler "error: multiple methods named 'keyCode' found with mismatched result, parameter type or attributes" when using WebKit in precompiled header

The possible methods named 'keyCode' are: NSEvent: -(unsigned short) keyCode DDHotKey: @property (nonatomic, setter = _setKeyCode:) unsigned short keyCode DOMUIEvent : @property(readonly) int keyCode

DOMUIEvent is int whereas DDHotKey and NSEvent is unsigned short