Add # COMPONENT to OWNERS

See https://tinyurl.com/yxau5sc4 for context.

Bug: 977050
Change-Id: If61a2791abc8654628acb5ed45185394256db72d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1808170Reviewed-by: Brian White <bcwhite@chromium.org>
Commit-Queue: Eric Foo <efoo@chromium.org>
Auto-Submit: Eric Foo <efoo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#698571}

components/tab_count_metrics/OWNERS

+# COMPONENT: Internals>Metrics
+# Use the above COMPONENT in crbugs to to file bugs against issues in this folder
+
 file://base/metrics/OWNERS