Add COMPONENT directive to os_crypt's OWNERS

This adds a COMPONENT directive to //components/os_crypt/OWNERS, which
points to the right crbug.com component for os_crypt. The COMPONENT
directive has been added to OWNERS files recently (an example is
//components/password_manager/OWNERS) and is useful for developers
when filing bugs about known code locations. It is especially useful
for os_crypt, because neither the crbug.com component name nor its
description mentions "os_crypt", so it might be hard to find just by a
query in crbug.com.

Bug: None
Change-Id: I56f1f8289db573118f41a622d09e69aed3029e42
Reviewed-on: https://chromium-review.googlesource.com/765450Reviewed-by: Christos Froussios <cfroussios@chromium.org>
Commit-Queue: Vaclav Brozek <vabr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#515909}

components/os_crypt/OWNERS

 cfroussios@chromium.org
 thestig@chromium.org
+
+# COMPONENT: Internals>LocalDataEncryption