Add WinrtWindow.cpp and WinRT version of angle_util Change-Id: If4ff4b966f5bd388d32c72a2d1bcf9cf29e6032d Reviewed-on: https://chromium-review.googlesource.com/297308 Reviewed-by: Geoff Lang <geofflang@chromium.org> Tested-by: Austin Kinross <aukinros@microsoft.com>