jni_generator: Add an OWNERS file.

Change-Id: I54c4f60513076030258b1b6b3a6a6e681f353578
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1632300
Auto-Submit: Eric Stevenson <estevenson@chromium.org>
Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Commit-Queue: Yaron Friedman <yfriedman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#663756}

base/android/jni_generator/OWNERS

+agrieve@chromium.org
+estevenson@chromium.org
+
+# COMPONENT: Build
\ No newline at end of file