Correctly support several consecutive stack modifications.

src/debug.h

 // 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 428 matching lines @@
     // No frame has been dropped.
     FRAMES_UNTOUCHED,
     // The top JS frame had been calling IC stub. IC stub mustn't be called now.
     FRAME_DROPPED_IN_IC_CALL,
     // The top JS frame had been calling debug break slot stub. Patch the
     // address this stub jumps to in the end.
     FRAME_DROPPED_IN_DEBUG_SLOT_CALL,
     // The top JS frame had been calling some C++ function. The return address
     // gets patched automatically.
     FRAME_DROPPED_IN_DIRECT_CALL,
-    FRAME_DROPPED_IN_RETURN_CALL
+    FRAME_DROPPED_IN_RETURN_CALL,
+    CURRENTLY_SET_MODE
   };
 
   void FramesHaveBeenDropped(StackFrame::Id new_break_frame_id,
                                     FrameDropMode mode,
                                     Object** restarter_frame_function_pointer);
 
   // Initializes an artificial stack frame. The data it contains is used for:
   //  a. successful work of frame dropper code which eventually gets control,
   //  b. being compatible with regular stack structure for various stack
   //     iterators.
@@ skipping 581 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(MessageDispatchHelperThread);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // ENABLE_DEBUGGER_SUPPORT
 
 #endif  // V8_DEBUG_H_