Add example to --unsafely-treat-insecure-origin-as-secure flag description

It's not obvious that just entering "localhost" in the
chrome://flags/#unsafely-treat-insecure-origin-as-secure input field won't
do anything.
This CL adds a small example showing the "http://" part is required.

Bug: 995002
Change-Id: Ic08ef53e67d397086abbf734facb437ec0717a2d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1771096Reviewed-by: Łukasz Anforowicz <lukasza@chromium.org>
Commit-Queue: Łukasz Anforowicz <lukasza@chromium.org>
Auto-Submit: Alan Cutter <alancutter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#690734}

chrome/browser/flag_descriptions.cc

@@ -1982,9 +1982,9 @@ const char kTreatInsecureOriginAsSecureName[] =
     "Insecure origins treated as secure";
 const char kTreatInsecureOriginAsSecureDescription[] =
     "Treat given (insecure) origins as secure origins. Multiple origins can be "
-    "supplied as a comma-separated list. For the definition of secure "
-    "contexts, "
-    "see https://w3c.github.io/webappsec-secure-contexts/";
+    "supplied as a comma-separated list. Origins must have their protocol "
+    "specified e.g. \"http://example.com\". For the definition of secure "
+    "contexts, see https://w3c.github.io/webappsec-secure-contexts/";
 
 const char kTreatUnsafeDownloadsAsActiveName[] =
     "Treat risky downloads over insecure connections as active mixed content";