Update fetch / loader classes to use OVERRIDE / FINAL when needed

Source/core/fetch/MemoryCache.h

Index: Source/core/fetch/MemoryCache.h
diff --git a/Source/core/fetch/MemoryCache.h b/Source/core/fetch/MemoryCache.h
index b85260e2e53893d23c889e0fc3fd6e027c455987..e263b0d07203a24722f9eeea1909cf345664ab81 100644
--- a/Source/core/fetch/MemoryCache.h
+++ b/Source/core/fetch/MemoryCache.h
@@ -59,7 +59,7 @@ struct SecurityOriginHash;
 // Enable this macro to periodically log information about the memory cache.
 #undef MEMORY_CACHE_STATS
 
-class MemoryCache : public blink::WebThread::TaskObserver {
+class MemoryCache FINAL : public blink::WebThread::TaskObserver {
     WTF_MAKE_NONCOPYABLE(MemoryCache); WTF_MAKE_FAST_ALLOCATED;
 public:
     MemoryCache();