Oilpan: Scale up the number of marking threads according to available processors

Source/platform/heap/CallbackStack.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CallbackStack_h
 #define CallbackStack_h
 
 #include "platform/heap/ThreadState.h"
 
 namespace blink {
@@ skipping 35 matching lines @@
 
     void append(CallbackStack*);
     void takeBlockFrom(CallbackStack*);
 
     void invokeEphemeronCallbacks(Visitor*);
 
 #if ENABLE(ASSERT)
     bool hasCallbackForObject(const void*);
 #endif
 
-    static const size_t blockSize = 200;
+    static const size_t blockSize = 128;
 
 private:
     class Block;
 
     void invokeOldestCallbacks(Block*, Block*, Visitor*);
     bool hasJustOneBlock() const;
     void swap(CallbackStack* other);
 
     Block* m_first;
     Block* m_last;
 };
 
 }
 
 #endif // CallbackStack_h