Better single stepping in VM debugger

runtime/vm/isolate.h

 // Copyright (c) 2013, 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_ISOLATE_H_
 #define VM_ISOLATE_H_
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "platform/thread.h"
@@ skipping 416 matching lines @@
   }
 
   static bool IsDeoptAfter(intptr_t deopt_id) {
     return (deopt_id % kDeoptIdStep) == kDeoptIdAfterOffset;
   }
 
   Mutex* mutex() const { return mutex_; }
 
   Debugger* debugger() const { return debugger_; }
 
+  void set_single_step(bool value) { single_step_ = value; }
+  bool single_step() const { return single_step_; }
+  static intptr_t single_step_offset() {
+    return OFFSET_OF(Isolate, single_step_);
+  }
+
   Simulator* simulator() const { return simulator_; }
   void set_simulator(Simulator* value) { simulator_ = value; }
 
   GcPrologueCallbacks& gc_prologue_callbacks() {
     return gc_prologue_callbacks_;
   }
 
   GcEpilogueCallbacks& gc_epilogue_callbacks() {
     return gc_epilogue_callbacks_;
   }
@@ skipping 194 matching lines @@
   Dart_Port main_port_;
   Heap* heap_;
   ObjectStore* object_store_;
   RawContext* top_context_;
   uword top_exit_frame_info_;
   void* init_callback_data_;
   Dart_LibraryTagHandler library_tag_handler_;
   ApiState* api_state_;
   StubCode* stub_code_;
   Debugger* debugger_;
+  bool single_step_;
   Simulator* simulator_;
   LongJump* long_jump_base_;
   TimerList timer_list_;
   intptr_t deopt_id_;
   Mutex* mutex_;  // protects stack_limit_ and saved_stack_limit_.
   uword stack_limit_;
   uword saved_stack_limit_;
   MessageHandler* message_handler_;
   uword spawn_data_;
   bool is_runnable_;
@@ skipping 223 matching lines @@
 
  private:
   Isolate::IsolateRunState saved_state_;
 
   DISALLOW_COPY_AND_ASSIGN(IsolateRunStateManager);
 };
 
 }  // namespace dart
 
 #endif  // VM_ISOLATE_H_