[debugger] remove step count parameter from prepare step.

test/mjsunit/debug-constructor.js

 // Copyright 2008 the V8 project authors. 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.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 17 matching lines @@
 // Flags: --expose-debug-as debug
 // Get the Debug object exposed from the debug context global object.
 Debug = debug.Debug
 
 // Simple function which collects a simple call graph.
 var call_graph = "";
 function listener(event, exec_state, event_data, data) {
   if (event == Debug.DebugEvent.Break)
   {
     call_graph += exec_state.frame().func().name();
-    exec_state.prepareStep();
+    exec_state.prepareStep(Debug.StepAction.StepIn);
   }
 };
 
 // Add the debug event listener.
 Debug.setListener(listener);
 
 // Test debug event for constructor.
 function a() {
   new c();
 }
@@ skipping 20 matching lines @@
 
 // Break point stops on "x = 1" and steps to "new c()" and then into c.
 Debug.setBreakPoint(b, 1);
 call_graph = "";
 b();
 Debug.clearStepping();  // Clear stepping as the listener leaves it on.
 assertEquals("bbccdcb", call_graph);
 
 // Get rid of the debug event listener.
 Debug.setListener(null);