Do not implicitly enable the scissor test for side-by-side FBOs The patch modifies the ANGLE_multiview specification so that issuing a Draw* command has undefined results for side-by-side FBOs if the scissor test is disabled. Also, clearing a side-by-side framebuffer will result in clearing the whole content of the specified buffers if the scissor test is disabled. StateManagerGL and FramebufferGL are modified to address this change in the spec. BUG=angleproject:2062 TEST=angle_end2end_tests Change-Id: I39a87d297944f12769dee2ead17b508ac22053db Reviewed-on: https://chromium-review.googlesource.com/612283 Commit-Queue: Martin Radev <mradev@nvidia.com> Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org>