WindowTest.cpp was missing <algorithm> for std::min and std::max.

BUG=angleproject:892

Change-Id: I9bf6e7b8e66cd4ffc34ee639f495b469dabde91a
Reviewed-on: https://chromium-review.googlesource.com/284590Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>