Oilpan: Mark the NodeList hierarchy MainThreadOnly

Source/platform/heap/ThreadState.h

Index: Source/platform/heap/ThreadState.h
diff --git a/Source/platform/heap/ThreadState.h b/Source/platform/heap/ThreadState.h
index 54e561338f10ccdbeae0478031f2e27c7411f688..9d2dd61018721f303bdd0dfe323ccaa70da73910 100644
--- a/Source/platform/heap/ThreadState.h
+++ b/Source/platform/heap/ThreadState.h
@@ -84,10 +84,15 @@ enum ThreadAffinity {
     MainThreadOnly,
 };
 
+// FIXME: These forward declarations violate dependency rules. Remove them.
+// Ideally we want to provide a USED_IN_MAIN_THREAD_ONLY(T) macro, which
+// indicates that classes in T's hierarchy are used only by the main thread.

[haraken, 2014/10/15 01:12:56]

I'm planning to address the FIXME by introducing GarbageCollectedOnMainThread in
a follow-up.

[tkent, 2014/10/15 03:34:39]

The GarbageCollectedOnMainThread approach sounds good.

 class Node;
-class CSSValue;
+class NodeList;
 
-template<typename T, bool derivesNode = WTF::IsSubclass<typename WTF::RemoveConst<T>::Type, Node>::value> struct DefaultThreadingTrait;
+template<typename T,
+    bool derivesNode = WTF::IsSubclass<typename WTF::RemoveConst<T>::Type, Node>::value

[tkent, 2014/10/15 03:34:39]

Now derivesNode is a wrong name.  It will be removed soon because of
GarbageCollectedOnMainThread, right?

[haraken, 2014/10/15 03:38:59]

Renamed it to mainThreadOnly.

+        || WTF::IsSubclass<typename WTF::RemoveConst<T>::Type, NodeList>::value> struct DefaultThreadingTrait;
 
 template<typename T>
 struct DefaultThreadingTrait<T, false> {