[media] Do not configure mipmaps in gles2_decoder_helper.

This fails on Mac when run in a headless content_shell.

Also fixes an incorrect thread post bug in VdaVideoDecoder.

Bug: 522298
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: I09d397ee108920fc35e8aadc45d9b47840eb8686
Reviewed-on: https://chromium-review.googlesource.com/1033834
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Frank Liberato <liberato@chromium.org>
Commit-Queue: Dan Sanders <sandersd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#554555}
4 files changed