Make VM debugger stop at every safe point

runtime/vm/debugger.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_DEBUGGER_H_
 #define VM_DEBUGGER_H_
 
 #include "include/dart_debugger_api.h"
 
 #include "vm/object.h"
@@ skipping 355 matching lines @@
   DebuggerStackTrace* stack_trace_;
 
   RemoteObjectCache* obj_cache_;
 
   SourceBreakpoint* src_breakpoints_;
   CodeBreakpoint* code_breakpoints_;
 
   // Tells debugger what to do when resuming execution after a breakpoint.
   ResumeAction resume_action_;
 
-  // If >= 0, last_bpt_line contains the line number of the last breakpoint
-  // location for which the breakpoint callback function was called.
-  intptr_t last_bpt_line_;
-
   // Do not call back to breakpoint handler if this flag is set.
   // Effectively this means ignoring breakpoints. Set when Dart code may
   // be run as a side effect of getting values of fields.
   bool ignore_breakpoints_;
 
   Dart_ExceptionPauseInfo exc_pause_info_;
 
   static BreakpointHandler* bp_handler_;
   static EventHandler* event_handler_;
 
   friend class Isolate;
   friend class SourceBreakpoint;
   DISALLOW_COPY_AND_ASSIGN(Debugger);
 };
 
 
 }  // namespace dart
 
 #endif  // VM_DEBUGGER_H_