Add agrieve as OWNERS for future chrome proguard flags

Change-Id: I7885292bd9d125c45fa7aec61f657df47c2c4fc6
Reviewed-on: https://chromium-review.googlesource.com/1087173
Commit-Queue: Yaron Friedman <yfriedman@chromium.org>
Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#564747}

chrome/android/java/OWNERS

-per-file proguard.flags=agrieve@chromium.org
+per-file *.flags=agrieve@chromium.org
 per-file *.grd*=twellington@chromium.org