Bug 1615480 - Part 1: Return a raw pointer from Get[Extant]BrowsingContext, r=kmag

The BrowsingContext is guaranteed to be being kept alive by
`nsFrameLoader::mBrowsingContext` and by the nsDocShell or RemoteBrowser object.
This improves the ergonomics of this helper method, which may help avoid misuse
of `mBrowsingContext`.

Differential Revision: https://phabricator.services.mozilla.com/D62957

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

dom/base/nsFrameLoader.cpp

@@ -3262,8 +3262,7 @@ already_AddRefed<nsILoadContext> nsFrameLoader::LoadContext() {
   return loadContext.forget();
 }
 
-already_AddRefed<BrowsingContext> nsFrameLoader::GetBrowsingContext() {
-  RefPtr<BrowsingContext> browsingContext;
+BrowsingContext* nsFrameLoader::GetBrowsingContext() {
   if (IsRemoteFrame()) {
     Unused << EnsureRemoteBrowser();
   } else if (mOwnerContent) {
@@ -3272,15 +3271,15 @@ already_AddRefed<BrowsingContext> nsFrameLoader::GetBrowsingContext() {
   return GetExtantBrowsingContext();
 }
 
-already_AddRefed<BrowsingContext> nsFrameLoader::GetExtantBrowsingContext() {
-  RefPtr<BrowsingContext> browsingContext;
+BrowsingContext* nsFrameLoader::GetExtantBrowsingContext() {
+  BrowsingContext* browsingContext = nullptr;
   if (mRemoteBrowser) {
     browsingContext = mRemoteBrowser->GetBrowsingContext();
   } else if (mDocShell) {
     browsingContext = mDocShell->GetBrowsingContext();
   }
   MOZ_ASSERT_IF(browsingContext, browsingContext == mBrowsingContext);
-  return browsingContext.forget();
+  return browsingContext;
 }
 
 void nsFrameLoader::InitializeBrowserAPI() {
@@ -3487,8 +3486,7 @@ void nsFrameLoader::SetWillChangeProcess() {
       // resilient. For the moment, though, the surrounding process switch code
       // is enough in flux that we're better off with a workable interim
       // solution.
-      MOZ_DIAGNOSTIC_ASSERT(mBrowsingContext ==
-                            RefPtr<BrowsingContext>(GetBrowsingContext()));
+      MOZ_DIAGNOSTIC_ASSERT(mBrowsingContext == GetBrowsingContext());
       RefPtr<CanonicalBrowsingContext> bc(mBrowsingContext->Canonical());
       bc->SetInFlightProcessId(browserParent->Manager()->ChildID());
       auto callback = [bc](auto) { bc->SetInFlightProcessId(0); };

dom/base/nsFrameLoader.h

@@ -152,8 +152,8 @@ class nsFrameLoader final : public nsStubMutationObserver,
 
   already_AddRefed<nsILoadContext> LoadContext();
 
-  already_AddRefed<mozilla::dom::BrowsingContext> GetBrowsingContext();
-  already_AddRefed<mozilla::dom::BrowsingContext> GetExtantBrowsingContext();
+  mozilla::dom::BrowsingContext* GetBrowsingContext();
+  mozilla::dom::BrowsingContext* GetExtantBrowsingContext();
 
   /**
    * Start loading the frame. This method figures out what to load

dom/base/nsFrameLoaderOwner.cpp

@@ -33,8 +33,7 @@ void nsFrameLoaderOwner::SetFrameLoader(nsFrameLoader* aNewFrameLoader) {
   mFrameLoader = aNewFrameLoader;
 }
 
-already_AddRefed<mozilla::dom::BrowsingContext>
-nsFrameLoaderOwner::GetBrowsingContext() {
+mozilla::dom::BrowsingContext* nsFrameLoaderOwner::GetBrowsingContext() {
   if (mFrameLoader) {
     return mFrameLoader->GetBrowsingContext();
   }

dom/base/nsFrameLoaderOwner.h

@@ -42,7 +42,7 @@ class nsFrameLoaderOwner : public nsISupports {
   already_AddRefed<nsFrameLoader> GetFrameLoader();
   void SetFrameLoader(nsFrameLoader* aNewFrameLoader);
 
-  already_AddRefed<mozilla::dom::BrowsingContext> GetBrowsingContext();
+  mozilla::dom::BrowsingContext* GetBrowsingContext();
 
   // Destroy (if it exists) and recreate our frameloader, based on new
   // remoteness requirements. This should follow the same path as