Perform glFlush only on NVIDIA platforms

EGL_EXT_image_flush_external is broken on NVIDIA and causes image
corruption.

corruption.

Bug: 833975
Test: Ran on nyan_big, samus and veyron_jerry and verified there is no
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Change-Id: I218bb111470e7db18906834f43fd1ad92f28b4bc
Reviewed-on: https://chromium-review.googlesource.com/1017236
Reviewed-by: Daniele Castagna <[email protected]>
Reviewed-by: Kenneth Russell <[email protected]>
Commit-Queue: Daniel Nicoara <[email protected]>
Cr-Commit-Position: refs/heads/master@{#552121}
7 files changed