Add basic infrastructure for protecting V8's heap when leaving the VM...

src/heap.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 255 matching lines @@
     return reinterpret_cast<Address>(&always_allocate_scope_depth_);
   }
 
   static Address* NewSpaceAllocationTopAddress() {
     return new_space_.allocation_top_address();
   }
   static Address* NewSpaceAllocationLimitAddress() {
     return new_space_.allocation_limit_address();
   }
 
+#ifdef ENABLE_HEAP_PROTECTION
+  // Protect/unprotect the heap by marking all spaces read-only/writable.
+  static void Protect();
+  static void Unprotect();
+#endif
+
   // Allocates and initializes a new JavaScript object based on a
   // constructor.
   // Returns Failure::RetryAfterGC(requested_bytes, space) if the allocation
   // failed.
   // Please note this does not perform a garbage collection.
   static Object* AllocateJSObject(JSFunction* constructor,
                                   PretenureFlag pretenure = NOT_TENURED);
 
   // Returns a deep copy of the JavaScript object.
   // Properties and elements are copied too.
@@ skipping 1012 matching lines @@
   int marked_count_;
 
   // The count from the end of the previous full GC.  Will be zero if there
   // was no previous full GC.
   int previous_marked_count_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_HEAP_H_