Oilpan: make Supplementable tracing more regular.

Source/platform/Supplementable.h

Index: Source/platform/Supplementable.h
diff --git a/Source/platform/Supplementable.h b/Source/platform/Supplementable.h
index a15d59cabe3ade8cb9958434e6fa48b60b83ee02..25f0cf7ccfe7883537e9ba671dcb6a05cccb5e41 100644
--- a/Source/platform/Supplementable.h
+++ b/Source/platform/Supplementable.h
@@ -100,13 +100,11 @@ struct SupplementableTraits;
 template<typename T>
 struct SupplementableTraits<T, true> {
     typedef RawPtr<SupplementBase<T, true> > SupplementArgumentType;
-    typedef HeapHashMap<const char*, Member<SupplementBase<T, true> >, PtrHash<const char*> > SupplementMap;
 };
 
 template<typename T>
 struct SupplementableTraits<T, false> {
     typedef PassOwnPtr<SupplementBase<T, false> > SupplementArgumentType;
-    typedef HashMap<const char*, OwnPtr<SupplementBase<T, false> >, PtrHash<const char*> > SupplementMap;
 };
 
 template<bool>
@@ -119,6 +117,12 @@ template<>
 class SupplementTracing<false> {
 public:
     virtual ~SupplementTracing() { }
+    // FIXME: Oilpan: this trace() method is only provided to minimize
+    // the use of ENABLE(OILPAN) for Supplements deriving from the
+    // transition type WillBeHeapSupplement<>.
+    //
+    // When that transition type is removed (or its use is substantially
+    // reduced), remove this dummy trace method also.
     virtual void trace(Visitor*) { }
 };
 
@@ -145,9 +149,32 @@ public:
     }
 };
 
+template<typename T, bool isGarbageCollected>
+class SupplementableTracing;
+
+template<typename T>
+class SupplementableTracing<T, true> : public GarbageCollectedMixin {
+public:
+    virtual void trace(Visitor* visitor)
+    {
+        visitor->trace(m_supplements);
+    }
+
+protected:
+    typedef HeapHashMap<const char*, Member<SupplementBase<T, true> >, PtrHash<const char*> > SupplementMap;
+    SupplementMap m_supplements;
+};
+
+template<typename T>
+class SupplementableTracing<T, false> {
+protected:
+    typedef HashMap<const char*, OwnPtr<SupplementBase<T, false> >, PtrHash<const char*> > SupplementMap;
+    SupplementMap m_supplements;
+};
+
 // Helper class for implementing Supplementable and HeapSupplementable.
 template<typename T, bool isGarbageCollected = false>
-class SupplementableBase {
+class SupplementableBase : public SupplementableTracing<T, isGarbageCollected> {
 public:
     void provideSupplement(const char* key, typename SupplementableTraits<T, isGarbageCollected>::SupplementArgumentType supplement)
     {
@@ -175,17 +202,6 @@ public:
 #endif
     }
 
-    // We have a trace method in the SupplementableBase class to ensure we have
-    // the vtable at the first word of the object. However we don't trace the
-    // m_supplements here, but in the partially specialized template subclasses
-    // since we only want to trace it for garbage collected classes.
-    virtual void trace(Visitor*) { }
-
-    // FIXME: Oilpan: Make private and remove this ignore once PersistentHeapSupplementable is removed again.
-protected:
-    GC_PLUGIN_IGNORE("")
-    typename SupplementableTraits<T, isGarbageCollected>::SupplementMap m_supplements;
-
 #if ENABLE(ASSERT)
 protected:
     SupplementableBase() : m_threadId(currentThread()) { }
@@ -195,38 +211,17 @@ private:
 #endif
 };
 
-// This class is used to make an on-heap class supplementable. Its supplements
-// must be HeapSupplement.
 template<typename T>
 class HeapSupplement : public SupplementBase<T, true> { };
 
-// FIXME: Oilpan: Move GarbageCollectedMixin to SupplementableBase<T, true> once PersistentHeapSupplementable is removed again.
 template<typename T>
-class GC_PLUGIN_IGNORE("http://crbug.com/395036") HeapSupplementable : public SupplementableBase<T, true>, public GarbageCollectedMixin {
-public:
-    virtual void trace(Visitor* visitor) OVERRIDE
-    {
-        visitor->trace(this->m_supplements);
-        SupplementableBase<T, true>::trace(visitor);
-    }
-};
+class HeapSupplementable : public SupplementableBase<T, true> { };
 
 template<typename T>
 class Supplement : public SupplementBase<T, false> { };
 
-// This class is used to make an off-heap class supplementable with off-heap
-// supplements (Supplement).
 template<typename T>
-class GC_PLUGIN_IGNORE("http://crbug.com/395036") Supplementable : public SupplementableBase<T, false> {
-public:
-    virtual void trace(Visitor* visitor)
-    {
-        // No tracing of off-heap supplements. We should not have any Supplementable
-        // object on the heap.
-        COMPILE_ASSERT(!IsGarbageCollectedType<T>::value, GarbageCollectedObjectMustBeHeapSupplementable);
-        SupplementableBase<T, false>::trace(visitor);
-    }
-};
+class Supplementable : public SupplementableBase<T, false> { };
 
 template<typename T>
 struct ThreadingTrait<SupplementBase<T, true> > {