Bug 1596768 - Remove GetBindingParent usage in layout. r=smaug

We only use it to escape out of NAC trees for ::selection pseudo-element.

Differential Revision: https://phabricator.services.mozilla.com/D53216

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

layout/generic/nsFrame.cpp

@@ -2357,7 +2357,7 @@ bool nsDisplaySelectionOverlay::CreateWebRenderCommands(
 static Element* FindElementAncestorForMozSelection(nsIContent* aContent) {
   NS_ENSURE_TRUE(aContent, nullptr);
   while (aContent && aContent->IsInNativeAnonymousSubtree()) {
-    aContent = aContent->GetBindingParent();
+    aContent = aContent->GetClosestNativeAnonymousSubtreeRootParent();
   }
   NS_ASSERTION(aContent, "aContent isn't in non-anonymous tree?");
   while (aContent && !aContent->IsElement()) {