Correctly support several consecutive stack modifications.

src/debug.cc

 // Copyright 2012 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 2299 matching lines @@
     }
     it.next();
   }
   return false;
 }
 
 
 void Debug::FramesHaveBeenDropped(StackFrame::Id new_break_frame_id,
                                   FrameDropMode mode,
                                   Object** restarter_frame_function_pointer) {
-  thread_local_.frame_drop_mode_ = mode;
+  if (mode != CURRENTLY_SET_MODE) {
+    thread_local_.frame_drop_mode_ = mode;
+  }
   thread_local_.break_frame_id_ = new_break_frame_id;
   thread_local_.restarter_frame_function_pointer_ =
       restarter_frame_function_pointer;
 }
 
 
 const int Debug::FramePaddingLayout::kInitialSize = 1;
 
 
 // Any even value bigger than kInitialSize as needed for stack scanning.
@@ skipping 1355 matching lines @@
     {
       Locker locker;
       Isolate::Current()->debugger()->CallMessageDispatchHandler();
     }
   }
 }
 
 #endif  // ENABLE_DEBUGGER_SUPPORT
 
 } }  // namespace v8::internal