shiny/driver/internal/win32: introduce and use ResizeClientRect

This CL makes screen.NewWindowOptions.Width and
screen.NewWindowOptions.Height parameters of screen.NewWindow
set window's client area of the specified window, instead of
setting dimensions of the bounding rectangle.

Fixes golang/go#19704.

Change-Id: Ic8a819e8127b89cc2734ed26dff6be06d2446ab1
Reviewed-on: https://go-review.googlesource.com/39111
Reviewed-by: Nigel Tao <nigeltao@golang.org>
4 files changed