add hiroshige@ to core/OWNERS

Bug: None
Change-Id: I034500f7ac6f551ddcb6b53a728796e9d55dd8a5
Reviewed-on: https://chromium-review.googlesource.com/958890Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Kouhei Ueno <kouhei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542726}

third_party/WebKit/Source/core/OWNERS

@@ -30,6 +30,7 @@ fs@opera.com
 futhark@chromium.org
 haraken@chromium.org
 hayato@chromium.org
+hiroshige@chromium.org
 ikilpatrick@chromium.org
 inferno@chromium.org
 japhet@chromium.org