Gets the width and height of the current window.

        :Usage:
            ::

                driver.get_window_size()

def get_window_size(self, windowHandle='current'):
        """
        Gets the width and height of the current window.

        :Usage:
            ::

                driver.get_window_size()
        """
        command = Command.GET_WINDOW_SIZE
        if self.w3c:
            if windowHandle != 'current':
                warnings.warn("Only 'current' window is supported for W3C compatibile browsers.")
            size = self.get_window_rect()
        else:
            size = self.execute(command, {'windowHandle': windowHandle})

        if size.get('value', None) is not None:
            size = size['value']

        return {k: size[k] for k in ('width', 'height')}