Bug 1675820 - Part 7: Fix marionette BrowsingContext replace detection logic, r=whimboo,marionette-reviewers,farre

Differential Revision: https://phabricator.services.mozilla.com/D108866

docshell/base/BrowsingContext.cpp

@@ -833,8 +833,14 @@ void BrowsingContext::Detach(bool aFromIPC) {
   }
 
   if (nsCOMPtr<nsIObserverService> obs = services::GetObserverService()) {
-    obs->NotifyObservers(ToSupports(this), "browsing-context-discarded",
-                         nullptr);
+    // Why the context is being discarded. This will always be "discard" in the
+    // content process, but may be "replace" if it's known the context being
+    // replaced in the parent process.
+    const char16_t* why = u"discard";
+    if (XRE_IsParentProcess() && IsTop() && !Canonical()->GetWebProgress()) {
+      why = u"replace";
+    }
+    obs->NotifyObservers(ToSupports(this), "browsing-context-discarded", why);
   }
 
   // NOTE: Doesn't use SetClosed, as it will be set in all processes

testing/marionette/navigate.js

@@ -313,10 +313,11 @@ navigate.waitForNavigationCompleted = async function waitForNavigationCompleted(
 
   // In the case when the currently selected frame is closed,
   // there will be no further load events. Stop listening immediately.
-  const onBrowsingContextDiscarded = (subject, topic) => {
-    // With the currentWindowGlobal gone the browsing context hasn't been
-    // replaced due to a remoteness change but closed.
-    if (subject == browsingContextFn() && !subject.currentWindowGlobal) {
+  const onBrowsingContextDiscarded = (subject, topic, why) => {
+    // If the BrowsingContext is being discarded to be replaced by another
+    // context, we don't want to stop waiting for the pageload to complete, as
+    // we will continue listening to the newly created context.
+    if (subject == browsingContextFn() && why != "replace") {
       logger.trace(
         "Canceled page load listener " +
           `because browsing context with id ${subject.id} has been removed`