Bug 1655765 - Add media permission for about:welcome privacy page mp4 r=ckerschb

Differential Revision: https://phabricator.services.mozilla.com/D85192

dom/html/HTMLMediaElement.cpp

@@ -1746,6 +1746,8 @@ class HTMLMediaElement::ChannelLoader final {
       securityFlags |= nsILoadInfo::SEC_COOKIES_INCLUDE;
     }
 
+    securityFlags |= nsILoadInfo::SEC_ALLOW_CHROME;
+
     MOZ_ASSERT(
         aElement->IsAnyOfHTMLElements(nsGkAtoms::audio, nsGkAtoms::video));
     nsContentPolicyType contentPolicyType =