[MIX-DL] Add link to blog post to console message.

This CL adds a link to the MIX-DL blog post to the console message
printed when mixed-content downloads occur. This had to wait until today
since, well, the blog posted wasn't posted until today.

Fixed: 1049133
Change-Id: Id3df23e2d4ab6f63e9c33b23155fa27a056378ab
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2042380
Commit-Queue: Joe DeBlasio <jdeblasio@chromium.org>
Commit-Queue: Mustafa Emre Acer <meacer@chromium.org>
Auto-Submit: Joe DeBlasio <jdeblasio@chromium.org>
Reviewed-by: Mustafa Emre Acer <meacer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#739063}

chrome/browser/download/mixed_content_download_blocking.cc

@@ -314,7 +314,10 @@ void PrintConsoleMessage(const MixedContentDownloadData& data,
           "Mixed Content: The site at '%s' was loaded over a secure "
           "connection, but the file at '%s' was %s an insecure "
           "connection. This file should be served over HTTPS. "
-          "This download %s.",
+          "This download %s. See "
+          "https://blog.chromium.org/2020/02/"
+          "protecting-users-from-insecure.html"
+          " for more details.",
           data.initiator_->GetURL().spec().c_str(),
           data.item_->GetURL().spec().c_str(),
           (data.is_redirect_chain_secure_ ? "loaded over"