LibWeb/HTML: Store NonnullGCPtr in browsing context set

These are never supposed to be null.

Userland/Libraries/LibWeb/HTML/BrowsingContext.cpp

@@ -80,7 +80,7 @@ JS::NonnullGCPtr<BrowsingContext> BrowsingContext::create_a_new_top_level_browsi
     auto group = BrowsingContextGroup::create_a_new_browsing_context_group(page);
 
     // 2. Return group's browsing context set[0].
-    return *(*group->browsing_context_set().begin());
+    return *group->browsing_context_set().begin();
 }
 
 // https://html.spec.whatwg.org/multipage/browsers.html#creating-a-new-browsing-context
@@ -858,7 +858,7 @@ void BrowsingContext::remove()
     set_group(nullptr);
 
     // 4. Remove browsingContext from group's browsing context set.
-    group->browsing_context_set().remove(this);
+    group->browsing_context_set().remove(*this);
 
     // 5. If group's browsing context set is empty, then remove group from the user agent's browsing context group set.
     // NOTE: This is done by ~BrowsingContextGroup() when the refcount reaches 0.

Userland/Libraries/LibWeb/HTML/BrowsingContextGroup.cpp

@@ -58,7 +58,7 @@ void BrowsingContextGroup::append(BrowsingContext& browsing_context)
     VERIFY(browsing_context.is_top_level());
 
     // 1. Append browsingContext to group's browsing context set.
-    m_browsing_context_set.set(&browsing_context);
+    m_browsing_context_set.set(browsing_context);
 
     // 2. Set browsingContext's group to group.
     browsing_context.set_group(this);

Userland/Libraries/LibWeb/HTML/BrowsingContextGroup.h

@@ -35,7 +35,7 @@ private:
     virtual void visit_edges(Cell::Visitor&) override;
 
     // https://html.spec.whatwg.org/multipage/browsers.html#browsing-context-group-set
-    OrderedHashTable<JS::GCPtr<BrowsingContext>> m_browsing_context_set;
+    OrderedHashTable<JS::NonnullGCPtr<BrowsingContext>> m_browsing_context_set;
 
     WeakPtr<Page> m_page;
 };