[Isolates] Avoid isolate lookup in HandleScope destructor.

src/handles-inl.h

 // Copyright 2006-2008 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 109 matching lines @@
     v8::ImplementationUtilities::HandleScopeData* previous) {
   v8::ImplementationUtilities::HandleScopeData* current =
       Isolate::Current()->handle_scope_data();
   *previous = *current;
   current->extensions = 0;
 }
 
 
 void HandleScope::Leave(
     const v8::ImplementationUtilities::HandleScopeData* previous) {
-  Isolate* isolate = Isolate::Current();
+  Isolate* isolate = previous->isolate;
+  ASSERT(isolate == Isolate::Current());
   v8::ImplementationUtilities::HandleScopeData* current =
       isolate->handle_scope_data();
   if (current->extensions > 0) {
     DeleteExtensions(isolate);
   }
   *current = *previous;
 #ifdef DEBUG
   ZapRange(current->next, current->limit);
 #endif
 }
@@ skipping 15 matching lines @@
   // Restore state in current handle scope to re-enable handle
   // allocations.
   Isolate::Current()->handle_scope_data()->extensions = extensions_;
 }
 #endif
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HANDLES_INL_H_