[inspector] migrate stepping related methods to debug-interface

src/debug/debug-interface.h

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_DEBUG_DEBUG_INTERFACE_H_
 #define V8_DEBUG_DEBUG_INTERFACE_H_
 
 #include "include/v8-debug.h"
 #include "include/v8.h"
 
@@ skipping 109 matching lines @@
   };
 
   /**
    * Defines if VM will pause on exceptions or not.
    * If BreakOnAnyExceptions is set then VM will pause on caught and uncaught
    * exception, if BreakOnUncaughtException is set then VM will pause only on
    * uncaught exception, otherwise VM won't stop on any exception.
    */
   static void ChangeBreakOnException(Isolate* isolate,
                                      ExceptionBreakState state);
+
+  enum StepAction {
+    StepOut = 0,   // Step out of the current function.
+    StepNext = 1,  // Step to the next statement in the current function.
+    StepIn = 2,    // Step into new functions invoked or the next statement
+                   // in the current function.
+    StepFrame = 3  // Step into a new frame or return to previous frame.
+  };
+
+  static void PrepareStep(Isolate* isolate, StepAction action);
+  static void ClearStepping(Isolate* isolate);
 };
 
 }  // namespace v8
 
 #endif  // V8_DEBUG_DEBUG_INTERFACE_H_