Allow stepping when paused at isolate start.

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_tools_api.h"
 
 #include "vm/object.h"
@@ skipping 441 matching lines @@
   void RemoveBreakpoint(intptr_t bp_id);
   Breakpoint* GetBreakpointById(intptr_t id);
 
   void SetStepOver();
   void SetSingleStep();
   void SetStepOut();
   bool IsStepping() const { return resume_action_ != kContinue; }
 
   bool IsPaused() const { return pause_event_ != NULL; }
 
+  // Put the isolate into single stepping mode when Dart code next runs.
+  //
+  // This is used by the vm service to allow the user to step while
+  // paused at isolate start.
+  void EnterSingleStepMode();
+
   // Indicates why the debugger is currently paused.  If the debugger
   // is not paused, this returns NULL.  Note that the debugger can be
   // paused for breakpoints, isolate interruption, and (sometimes)
   // exceptions.
   const DebuggerEvent* PauseEvent() const { return pause_event_; }
 
   void SetExceptionPauseInfo(Dart_ExceptionPauseInfo pause_info);
   Dart_ExceptionPauseInfo GetExceptionPauseInfo() const;
 
   void VisitObjectPointers(ObjectPointerVisitor* visitor);
@@ skipping 172 matching lines @@
 
   friend class Isolate;
   friend class BreakpointLocation;
   DISALLOW_COPY_AND_ASSIGN(Debugger);
 };
 
 
 }  // namespace dart
 
 #endif  // VM_DEBUGGER_H_