Make debugger unloading deferred operation

src/debug.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 636 matching lines @@
 
   // Unload the debugger if possible. Only called when no debugger is currently
   // active.
   static void UnloadDebugger();
 
   inline static bool EventActive(v8::DebugEvent event) {
     ScopedLock with(debugger_access_);
 
     // Check whether the message handler was been cleared.
     if (debugger_unload_pending_) {
-      UnloadDebugger();
+      if (Debug::debugger_entry() == NULL) {
+        UnloadDebugger();
+      }
     }
 
     // Currently argument event is not used.
     return !compiling_natives_ && Debugger::IsDebuggerActive();
   }
 
   static void set_compiling_natives(bool compiling_natives) {
     Debugger::compiling_natives_ = compiling_natives;
   }
   static bool compiling_natives() { return Debugger::compiling_natives_; }
@@ skipping 189 matching lines @@
   Debug::AddressId id_;
   int reg_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // ENABLE_DEBUGGER_SUPPORT
 
 #endif  // V8_DEBUG_H_