Add jbauman as OWNER of GPU process and command buffer related infrastructure.

John understands the infrastructure at a deep level and will provide
good code reviews and nominate others appropriately.

BUG=none
R=piman@chromium.org

Review URL: https://codereview.chromium.org/510173002

Cr-Commit-Position: refs/heads/master@{#292262}

content/browser/gpu/OWNERS

+jbauman@chromium.org
 kbr@chromium.org
 piman@chromium.org
 zmo@chromium.org

content/common/gpu/OWNERS

+jbauman@chromium.org
 kbr@chromium.org
 piman@chromium.org
 sievers@chromium.org

content/gpu/OWNERS

-kbr@chromium.org
-piman@chromium.org
+jbauman@chromium.org
+kbr@chromium.org
+piman@chromium.org

content/renderer/gpu/OWNERS

+jbauman@chromium.org
 kbr@chromium.org
 piman@chromium.org