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Adapted the v4l2 video decoder to make use of the GLFenceEGL wrapper, rather
than using EGLSync functionality directly.

Benefits:
* Better code reuse and less code duplication.
* Makes it easier to mock out dependencies when unit testing.
* Easier to swap to different implementation if required.

TEST=ran VDA tests on peach-pi

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: If3f9ab3668bb9e6764b983557e8d9ccd6b3c2cf7
Reviewed-on: https://chromium-review.googlesource.com/1195203
Commit-Queue: David Staessens <dstaessens@chromium.org>
Reviewed-by: Pawel Osciak <posciak@chromium.org>
Reviewed-by: Hirokazu Honda <hiroh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589392}