Add agable@ to //infra/OWNERS.

R=jbudorick, dpranke, tikuta, agable

Change-Id: Ia2a8f2965781fc2d71f14f3142f6e8e155d49dc9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1728038Reviewed-by: John Budorick <jbudorick@chromium.org>
Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Aaron Gable <agable@chromium.org>
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#682754}

infra/OWNERS

 # This is reserved for people that are comfortable with Chromium builders
 # and understand the implications of changing their configurations.
 
+agable@chromium.org
 bpastene@chromium.org
 dpranke@chromium.org
 hans@chromium.org