Add jdeblasio@ as owner of mixed content download blocking.

This CL adds jdeblasio@ as an owner only of
chrome/browser/download/mixed_content_download_blocking*.

Bug: 973214
Change-Id: Ib7a32152e9f05ac32c6c99b780275c0cc5bfc737
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1932467Reviewed-by: Min Qin <qinmin@chromium.org>
Commit-Queue: Joe DeBlasio <jdeblasio@chromium.org>
Cr-Commit-Position: refs/heads/master@{#718692}

chrome/browser/download/OWNERS

@@ -2,5 +2,6 @@ file://components/download/OWNERS
 
 per-file download_dir_policy_handler*=atwilson@chromium.org
 per-file download_request_limiter*=dominickn@chromium.org
+per-file mixed_content_download_blocking*=jdeblasio@chromium.org
 
 # COMPONENT: UI>Browser>Downloads