[debugger] remove step count parameter from prepare step.

test/mjsunit/debug-stepframe.js

 // Copyright 2014 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
 
 function f0() {
   var v00 = 0;              // Break 1
   var v01 = 1;
   // Normal function call in a catch scope.
@@ skipping 64 matching lines @@
 
 var b0 = f3.bind(o);
 
 var o = {};
 Object.defineProperty(o, "get", { get : get });
 Object.defineProperty(o, "set", { set : set });
 
 Debug = debug.Debug;
 var break_count = 0
 var exception = null;
-var step_size;
 
 function listener(event, exec_state, event_data, data) {
   if (event != Debug.DebugEvent.Break) return;
   try {
     var line = exec_state.frame(0).sourceLineText();
     print(line);
     var match = line.match(/\/\/ Break (\d+)$/);
     assertEquals(2, match.length);
     assertEquals(break_count, parseInt(match[1]));
-    break_count += step_size;
-    exec_state.prepareStep(Debug.StepAction.StepFrame, step_size);
+    break_count ++;
+    exec_state.prepareStep(Debug.StepAction.StepFrame);
   } catch (e) {
     print(e + e.stack);
     exception = e;
   }
 }
 
-for (step_size = 1; step_size < 6; step_size++) {
-  print("step size = " + step_size);
-  break_count = 0;
-  Debug.setListener(listener);
-  debugger;                 // Break 0
-  f0();
-  Debug.setListener(null);  // Break 16
-  assertTrue(break_count > 14);
-}
+
+break_count = 0;
+Debug.setListener(listener);
+debugger;                 // Break 0
+f0();
+Debug.setListener(null);  // Break 16
+assertTrue(break_count > 14);
 
 assertNull(exception);