Make __proto__ a real JavaScript accessor property.

test/mjsunit/proto-poison.js

 // Copyright 2013 the V8 project authors. All rights reserved.
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 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-#ifndef V8_MARKING_THREAD_H_
-#define V8_MARKING_THREAD_H_
+// Check that the __proto__ accessor is properly poisoned when extracted
+// from Object.prototype using the property descriptor.
+var desc = Object.getOwnPropertyDescriptor(Object.prototype, "__proto__");
+assertEquals("function", typeof desc.get);
+assertEquals("function", typeof desc.set);
+assertThrows("desc.get.call({})", TypeError);
+assertThrows("desc.set.call({})", TypeError);
 
-#include "atomicops.h"
-#include "flags.h"
-#include "platform.h"
-#include "v8utils.h"
-
-#include "spaces.h"
-
-#include "heap.h"
-
-namespace v8 {
-namespace internal {
-
-class MarkingThread : public Thread {
- public:
-  explicit MarkingThread(Isolate* isolate);
-
-  void Run();
-  void Stop();
-  void StartMarking();
-  void WaitForMarkingThread();
-
-  ~MarkingThread() {
-    delete start_marking_semaphore_;
-    delete end_marking_semaphore_;
-    delete stop_semaphore_;
-  }
-
- private:
-  Isolate* isolate_;
-  Heap* heap_;
-  Semaphore* start_marking_semaphore_;
-  Semaphore* end_marking_semaphore_;
-  Semaphore* stop_semaphore_;
-  volatile AtomicWord stop_thread_;
-  int id_;
-  static Atomic32 id_counter_;
-};
-
-} }  // namespace v8::internal
-
-#endif  // V8_MARKING_THREAD_H_
+// Check that any redefinition of the __proto__ accessor causes poising
+// to cease and the accessor to be extracted normally.
+Object.defineProperty(Object.prototype, "__proto__", { get:function(){} });
+desc = Object.getOwnPropertyDescriptor(Object.prototype, "__proto__");
+assertDoesNotThrow("desc.get.call({})");
+assertThrows("desc.set.call({})", TypeError);
+Object.defineProperty(Object.prototype, "__proto__", { set:function(x){} });
+desc = Object.getOwnPropertyDescriptor(Object.prototype, "__proto__");
+assertDoesNotThrow("desc.get.call({})");
+assertDoesNotThrow("desc.set.call({})");