Bad cast under CachedResourceLoader::preload()

https://bugs.webkit.org/show_bug.cgi?id=268405
rdar://121745788

Reviewed by Brent Fulgham.

In CachedResourceLoader::preload() we were calling requestResource(type)
to get a resource. Then if the type we requested was `FontResource`, we
assumed the the CachedResource returned was a CachedFont and would cast
to that type. However, this cast ends up being incorrect in some cases.
I suspect this could happen when requesting resources with the same URL
but different types.

To address the issue, we now check the actual type of the returned
CachedResource before casting it.

* Source/WebCore/loader/cache/CachedResourceLoader.cpp:
(WebCore::CachedResourceLoader::preload):

Originally-landed-as: 272448.421@safari-7618-branch (25c1145). rdar://124554524
Canonical link: https://commits.webkit.org/276162@main

Source/WebCore/loader/cache/CachedResourceLoader.cpp

@@ -1681,8 +1681,8 @@ ResourceErrorOr<CachedResourceHandle<CachedResource>> CachedResourceLoader::prel
     if (resource && (!m_preloads || !m_preloads->contains(*resource.value().get()))) {
         CachedResourceHandle resourceValue = resource.value();
         // Fonts need special treatment since just creating the resource doesn't trigger a load.
-        if (type == CachedResource::Type::FontResource)
-            downcast<CachedFont>(resourceValue.get())->beginLoadIfNeeded(*this);
+        if (CachedResourceHandle cachedFont = dynamicDowncast<CachedFont>(resourceValue.get()))
+            cachedFont->beginLoadIfNeeded(*this);
         resourceValue->increasePreloadCount();
 
         if (!m_preloads)