Bug 1739685 - part1 : copy `ShouldDelayMediaFromStart` in `ReplacedBy()` . r=emilio

A follow-up based on [1].

[1]
https://phabricator.services.mozilla.com/D128126#4226792
https://bugzilla.mozilla.org/show_bug.cgi?id=1733902#c12

Differential Revision: https://phabricator.services.mozilla.com/D130292

docshell/base/CanonicalBrowsingContext.cpp

@@ -304,6 +304,7 @@ void CanonicalBrowsingContext::ReplacedBy(
   txn.SetHistoryID(GetHistoryID());
   txn.SetExplicitActive(GetExplicitActive());
   txn.SetHasRestoreData(GetHasRestoreData());
+  txn.SetShouldDelayMediaFromStart(GetShouldDelayMediaFromStart());
   if (aNewContext->EverAttached()) {
     MOZ_ALWAYS_SUCCEEDS(txn.Commit(aNewContext));
   } else {