chrome/gpu: Change chrome/gpu/OWNERS

TBR=xhwang@chromium.org

Bug: None
Test: None
Change-Id: I215889e5ab8c25577c04e164a657c3b6f027a5f3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1731638
Commit-Queue: Hirokazu Honda <hiroh@chromium.org>
Reviewed-by: Pawel Osciak <posciak@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683472}

chrome/gpu/OWNERS

-kcwu@chromium.org
-posciak@chromium.org
+file://components/arc/video_accelerator/OWNERS
+file://media/OWNERS
+
+per-file chrome_content_gpu_client*=file://components/arc/video_accelerator/OWNERS
+per-file widevine_cdm_proxy*=file://media/OWNERS