Use EGLWindow in ANGLETests. This completes the refactor to use the same code for EGL and OS Window creation for samples and tests. BUG=angle:730 TEST=angle_tests Change-Id: Ib6de89f5bf83c0730a66f662cd1f87351f36a5f7 Reviewed-on: https://chromium-review.googlesource.com/213297 Tested-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>