Bug 1601779 - Don't process switch when we actually abort a channel load. r=kmag

We currently do a process switch for a failed load so that we show an error page in the right process. This adds an exception for loads that we just explicitly cancelled, since it shouldn't be necessary, and so that tests that use BrowserUtils.waitForDocLoadAndStopIt don't get confused.

Differential Revision: https://phabricator.services.mozilla.com/D58889

--HG--
extra : moz-landing-system : lando

netwerk/ipc/DocumentLoadListener.cpp

@@ -937,9 +937,11 @@ DocumentLoadListener::OnStartRequest(nsIRequest* aRequest) {
   // SessionStore.jsm. This will determine if a new process needs to be
   // spawned and if so SwitchProcessTo() will be called which will set a
   // ContentProcessIdPromise.
-  nsCOMPtr<nsIObserverService> obsService = services::GetObserverService();
-  obsService->NotifyObservers(ToSupports(this), "channel-on-may-change-process",
-                              nullptr);
+  if (status != NS_BINDING_ABORTED) {
+    nsCOMPtr<nsIObserverService> obsService = services::GetObserverService();
+    obsService->NotifyObservers(ToSupports(this),
+                                "channel-on-may-change-process", nullptr);
+  }
 
   if (mRedirectContentProcessIdPromise) {
     TriggerCrossProcessSwitch();