Vulkan: Create a pre-rotation test for 400x300 windows
Vulkan: Create a pre-rotation test for 400x300 windows

This test reproduces the cause of the failures with the
following dEQP tests:

dEQP.GLES31/functional_texture_multisample_samples_*_sample_position

This CL also fixes a problem with the previous test, and puts
the common rendering/ReadPixels code in a common method.

Bug: b/156395519
Change-Id: Id38476b6caf6f25c52f7504187fb500a39109438
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2207550
Reviewed-by: Courtney Goeltzenleuchter <aa371ec5c940a0ded89f7ed95bce84faebcf51df@google.com>
Reviewed-by: Geoff Lang <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>
Commit-Queue: Ian Elliott <ac50c12f27752fd82643b0b72adab33538bb2c97@google.com>

ppy/angle,ppy/angle,ppy/angle,ppy/angle