Bug 1506852 - Make sure to also clear opener in BrowsingContext. r=peterv

When calling nsGlobalWindowOuter::SetOpenerWindow with null we should
make sure to also clear BrowsingContext::mOpener.

Differential Revision: https://phabricator.services.mozilla.com/D11769

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

dom/base/nsGlobalWindowOuter.cpp

@@ -2266,11 +2266,11 @@ nsGlobalWindowOuter::SetOpenerWindow(nsPIDOMWindowOuter* aOpener,
   mOpener = opener.forget();
   NS_ASSERTION(mOpener || !aOpener, "Opener must support weak references!");
 
-  if (mDocShell && aOpener) {
+  if (mDocShell) {
     // TODO(farre): Here we really wish to only consider the case
     // where 'aOriginalOpener' is false, and we also really want to
     // move opener entirely to BrowsingContext. See bug 1502330.
-    GetBrowsingContext()->SetOpener(aOpener->GetBrowsingContext());
+    GetBrowsingContext()->SetOpener(aOpener ? aOpener->GetBrowsingContext() : nullptr);
   }
 
   // Check that the js visible opener matches! We currently don't depend on this