Add test coverage for BlitGL 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/1030171 Reviewed-by: Corentin Wallez <cwallez@chromium.org> Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>