Debugger: PreservePositionScope should clear positions inside the scope.

src/assembler.h

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // 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.
 //
@@ skipping 1094 matching lines @@
   friend class PreservePositionScope;
 
   DISALLOW_COPY_AND_ASSIGN(PositionsRecorder);
 };
 
 
 class PreservePositionScope BASE_EMBEDDED {
  public:
   explicit PreservePositionScope(PositionsRecorder* positions_recorder)
       : positions_recorder_(positions_recorder),
-        saved_state_(positions_recorder->state_) {}
+        saved_state_(positions_recorder->state_) {
+    // Reset positions so that previous ones do not accidentally get
+    // recorded within this scope.
+    positions_recorder->state_ = PositionState();
+  }
 
   ~PreservePositionScope() {
     positions_recorder_->state_ = saved_state_;
   }
 
  private:
   PositionsRecorder* positions_recorder_;
   const PositionState saved_state_;
 
   DISALLOW_COPY_AND_ASSIGN(PreservePositionScope);
@@ skipping 37 matching lines @@
   NullCallWrapper() { }
   virtual ~NullCallWrapper() { }
   virtual void BeforeCall(int call_size) const { }
   virtual void AfterCall() const { }
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_ASSEMBLER_H_