Avoid TLS load in AstNode constructor.

src/zone.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 56 matching lines @@
 
   // Delete all objects and free all memory allocated in the Zone.
   void DeleteAll();
 
   // Returns true if more memory has been allocated in zones than
   // the limit allows.
   inline bool excess_allocation();
 
   inline void adjust_segment_bytes_allocated(int delta);
 
+  inline Isolate* isolate() { return isolate_; }
+
   static unsigned allocation_size_;
 
  private:
   friend class Isolate;
   friend class ZoneScope;
 
   // All pointers returned from New() have this alignment.
   static const int kAlignment = kPointerSize;
 
   // Never allocate segments smaller than this size in bytes.
@@ skipping 144 matching lines @@
  public:
   ZoneSplayTree()
       : SplayTree<Config, ZoneListAllocationPolicy>() {}
   ~ZoneSplayTree();
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_ZONE_H_