Add mattm as OWNER for chrome/browser/certificate_manager_model*

Change-Id: Ide9ed87b0976edbdfc9d14cbed10e073391d4613
Reviewed-on: https://chromium-review.googlesource.com/1185421Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585263}

chrome/browser/OWNERS

@@ -18,6 +18,8 @@ per-file browser_close_manager_browsertest.cc=creis@chromium.org
 per-file browser_navigator_browsertest.*=alexmos@chromium.org
 per-file browser_navigator_browsertest.*=file://content/OWNERS
 
+per-file certificate_manager_model*=mattm@chromium.org
+
 per-file chrome_content_browser_client.cc=*
 per-file chrome_content_browser_client.h=*
 per-file chrome_content_browser_client_browsertest.cc=*