blink: Fix LinkLoader::FinishObserver to inherit from correct GCed class

Bug: 991989
Change-Id: Ib1e4102664a9be9e110199e386c31aaae7271702
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1743732Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Cr-Commit-Position: refs/heads/master@{#685243}

third_party/blink/renderer/core/loader/link_loader.cc

@@ -80,7 +80,7 @@ LinkLoader* LinkLoader::Create(LinkLoaderClient* client) {
 }
 
 class LinkLoader::FinishObserver final
-    : public GarbageCollectedFinalized<ResourceFinishObserver>,
+    : public GarbageCollectedFinalized<LinkLoader::FinishObserver>,
       public ResourceFinishObserver {
   USING_GARBAGE_COLLECTED_MIXIN(FinishObserver);
   USING_PRE_FINALIZER(FinishObserver, ClearResource);