Fix Win32Window::resize breaking angle_tests. We were messing up the client rect on resize, which caused the ReadPixels checks to mess up around the window edges. Disabling the window styles on the test windows masked this bug. Fix this by using a style-less child window inside the parent window. This gives us access to window styles for the samples project, along with the ability to use tiny 1x1 windows for testing. BUG=angle:730 Change-Id: Ic6dd931df7b4e32fbbcacbb004d3bbc49917f658 Reviewed-on: https://chromium-review.googlesource.com/217024 Tested-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>