Update OWNERS for file_manager.

Bug: None
Test: None
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I0985fa3b5678159d51b5e88342abf570bbe7818a
Reviewed-on: https://chromium-review.googlesource.com/917926Reviewed-by: Yuki Awano <yawano@chromium.org>
Commit-Queue: Naoki Fukino <fukino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#536688}

chrome/browser/chromeos/extensions/file_manager/OWNERS

@@ -2,4 +2,5 @@
 fukino@chromium.org
 hirono@chromium.org
 kinaba@chromium.org
+yamaguchi@chromium.org
 yoshiki@chromium.org

chrome/browser/chromeos/file_manager/OWNERS

 fukino@chromium.org
 hirono@chromium.org
 kinaba@chromium.org
+yamaguchi@chromium.org
 yoshiki@chromium.org

chrome/browser/resources/chromeos/zip_archiver/OWNERS

+yamaguchi@chromium.org
 yawano@chromium.org

ui/file_manager/OWNERS

@@ -2,5 +2,6 @@ fukino@chromium.org
 hirono@chromium.org
 mtomasz@chromium.org
 oka@chromium.org
+yamaguchi@chromium.org
 yawano@chromium.org
 yoshiki@chromium.org