[debugger] remove step count parameter from prepare step.

test/mjsunit/debug-liveedit-stepin.js

 // Copyright 2015 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.
 
 // Flags: --expose-debug-as debug
 
 Debug = debug.Debug
 
 function BestEditor() {
   var best_editor = "Emacs";
@@ skipping 16 matching lines @@
         case 1:
           Replace(BestEditor, "Emacs", "Eclipse");
           break;
         case 2:
           Replace(BestEditor, "Eclipse", "Vim");
           break;
         default:
           assertUnreachable();
       }
     }
-    exec_state.prepareStep(Debug.StepAction.StepIn, 1);
+    exec_state.prepareStep(Debug.StepAction.StepIn);
   } catch (e) {
     exception = e;
   }
 };
 
 function Replace(fun, original, patch) {
   var script = Debug.findScript(fun);
   if (fun.toString().indexOf(original) < 0) return;
   var patch_pos = script.source.indexOf(original);
   var change_log = [];
@@ skipping 24 matching lines @@
   "  return best_editor;","}",
   "results.push(BestEditor());",
   "results.push(BestEditor());",
   "  var best_editor = \"Eclipse\";",
   "  return best_editor;",
   "  var best_editor = \"Vim\";",
   "  return best_editor;",
   "}","results.push(BestEditor());",
   "Debug.setListener(null);"
 ], log);