Scaling and flipping of the framebuffer with blitFramebuffer are now
covered by end2end_tests. The test configurations are set so that the
BlitGL shader-based blit is also covered.

The tests reveal a bug in the D3D11 backend implementation of
blitFramebuffer when using an oversized source area.

BUG=angleproject:2486
BUG=angleproject:2519
BUG=angleproject:2521
TEST=angle_end2end_tests

Change-Id: Ica48e564a5b4180241ec4c4c6be06c58cc6dc29b
Reviewed-on: https://chromium-review.googlesource.com/1030171Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>