[Isolates] Minimize TLS accesses during startup deserialization.

src/serialize.h

 // Copyright 2006-2009 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 295 matching lines @@
   virtual void VisitRuntimeEntry(RelocInfo* rinfo) {
     UNREACHABLE();
   }
 
   void ReadChunk(Object** start, Object** end, int space, Address address);
   HeapObject* GetAddressFromStart(int space);
   inline HeapObject* GetAddressFromEnd(int space);
   Address Allocate(int space_number, Space* space, int size);
   void ReadObject(int space_number, Space* space, Object** write_back);
 
+  // Cached current isolate.
+  Isolate* isolate_;
+
   // Keep track of the pages in the paged spaces.
   // (In large object space we are keeping track of individual objects
   // rather than pages.)  In new space we just need the address of the
   // first object and the others will flow from that.
   List<Address> pages_[SerializerDeserializer::kNumberOfSpaces];
 
   SnapshotByteSource* source_;
   // This is the address of the next object that will be allocated in each
   // space.  It is used to calculate the addresses of back-references.
   Address high_water_[LAST_SPACE + 1];
@@ skipping 250 matching lines @@
   virtual int RootIndex(HeapObject* o) { return kInvalidRootIndex; }
   virtual bool ShouldBeInThePartialSnapshotCache(HeapObject* o) {
     return false;
   }
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_SERIALIZE_H_