In RendererD3D::createRenderTarget, we use getNearestSamples(samples)'s
result to assign D3D11_TEXTURE2D_DESC.SampleDesc.Count. However, in
renderer11::updateState, we used the original samples to calculate mask
by GetBlendSampleMask not the supported nearest samples. It would result
that multisample rendering result was incorrect when enable
AMPLE_COVERAGE and the samples is not in the suported list but less than
max samples. At least, on Intel Win platform, we can reproduce it.
The fixing is to use same samples in these two places.

BUG=angleproject:1610
TEST=MultisampleCompatibilityTest.DrawCoverageAndResolve

Change-Id: I255b12d1032317145adfcee94e65e88ae5307113
Reviewed-on: https://chromium-review.googlesource.com/408516Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>