Bug 1542790 - Part 2: Use BC::GetParent and BC::GetTop for local windows, r=peterv

This is required to support getting the `parent` and `top` properties from
within remote subframes.

Differential Revision: https://phabricator.services.mozilla.com/D26559

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

docshell/base/BrowsingContext.cpp

@@ -630,6 +630,10 @@ void BrowsingContext::Blur(ErrorResult& aError) {
 }
 
 Nullable<WindowProxyHolder> BrowsingContext::GetTop(ErrorResult& aError) {
+  if (mClosed) {
+    return nullptr;
+  }
+
   // We never return null or throw an error, but the implementation in
   // nsGlobalWindow does and we need to use the same signature.
   return WindowProxyHolder(Top());

dom/base/nsGlobalWindowOuter.cpp

@@ -2944,13 +2944,8 @@ bool nsPIDOMWindowOuter::GetServiceWorkersTestingEnabled() {
 }
 
 Nullable<WindowProxyHolder> nsGlobalWindowOuter::GetParentOuter() {
-  nsPIDOMWindowOuter* parent = GetScriptableParent();
-  BrowsingContext* parentBC;
-  if (!parent || !(parentBC = parent->GetBrowsingContext())) {
-    return nullptr;
-  }
-
-  return WindowProxyHolder(parentBC);
+  BrowsingContext* bc = GetBrowsingContext();
+  return bc ? bc->GetParent(IgnoreErrors()) : nullptr;
 }
 
 /**
@@ -3954,12 +3949,8 @@ uint32_t nsGlobalWindowOuter::Length() {
 }
 
 Nullable<WindowProxyHolder> nsGlobalWindowOuter::GetTopOuter() {
-  nsCOMPtr<nsPIDOMWindowOuter> top = GetScriptableTop();
-  BrowsingContext* topBC;
-  if (!top || !(topBC = top->GetBrowsingContext())) {
-    return nullptr;
-  }
-  return WindowProxyHolder(topBC);
+  BrowsingContext* bc = GetBrowsingContext();
+  return bc ? bc->GetTop(IgnoreErrors()) : nullptr;
 }
 
 already_AddRefed<BrowsingContext> nsGlobalWindowOuter::GetChildWindow(