Oilpan: disable conservative GCs during initial GC mixin construction.

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 3679356d36122a6d2663f34d95b126db10e55d0e..7229ba48968d94c8938de70a9611d3cd42e11468 100644
--- a/Source/platform/heap/ThreadState.h
+++ b/Source/platform/heap/ThreadState.h
@@ -582,6 +582,17 @@ public:
 
     double collectionRate() const { return m_collectionRate; }
 
+    // By entering a gc-forbidden scope, conservative GCs will not
+    // be allowed while handling an out-of-line allocation request.
+    // Intended used when constructing subclasses of GC mixins, where
+    // the object being constructed cannot be safely traced & marked
+    // fully should a GC be allowed while its subclasses are being
+    // constructed.
+    void enterGCForbiddenScope(unsigned delta)
+    {
+        m_gcForbiddenCount += delta;
+    }
+
 private:
     ThreadState();
     ~ThreadState();
@@ -626,14 +637,7 @@ private:
     void snapshotFreeList();
 #endif
 
-    // By entering a gc-forbidden scope, conservative GCs will not
-    // be allowed while handling an out-of-line allocation request.
-    // Intended used when constructing subclasses of GC mixins, where
-    // the object being constructed cannot be safely traced & marked
-    // fully should a GC be allowed while its subclasses are being
-    // constructed.
-    template<typename U, typename V> friend class AllocateObjectTrait;
-    void enterGCForbiddenScope() { m_gcForbiddenCount++; }
+    template<typename U> friend class GarbageCollectedMixinConstructorMarker;
     void leaveGCForbiddenScope()
     {
         ASSERT(m_gcForbiddenCount > 0);