[debugger] remove step count parameter from prepare step.

test/mjsunit/es6/debug-stepin-microtasks.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: --harmony-object-observe
 // Flags: --allow-natives-syntax --expose-debug-as debug
 
 Debug = debug.Debug
 var exception = null;
 var break_count = 0;
 var expected_breaks = -1;
 
 function listener(event, exec_state, event_data, data) {
   try {
     if (event == Debug.DebugEvent.Break) {
       assertTrue(exec_state.frameCount() != 0, "FAIL: Empty stack trace");
       if (!break_count) {
         // Count number of expected breakpoints in this source file.
         var source_text = exec_state.frame(0).func().script().source();
         expected_breaks = source_text.match(/\/\/\s*Break\s+\d+\./g).length;
         print("Expected breaks: " + expected_breaks);
       }
       var source = exec_state.frame(0).sourceLineText();
       print("paused at: " + source);
       assertTrue(source.indexOf("// Break " + break_count + ".") > 0,
                  "Unexpected pause at: " + source + "\n" +
                  "Expected: // Break " + break_count + ".");
       if (source.indexOf("StepOver.") !== -1) {
-        exec_state.prepareStep(Debug.StepAction.StepNext, 1);
+        exec_state.prepareStep(Debug.StepAction.StepNext);
       } else {
-        exec_state.prepareStep(Debug.StepAction.StepIn, 1);
+        exec_state.prepareStep(Debug.StepAction.StepIn);
       }
       ++break_count;
     }
   } catch (e) {
     exception = e;
     print(e, e.stack);
   }
 };
 
 Debug.setListener(listener);
@@ skipping 51 matching lines @@
     if (expected_breaks !== break_count) {
       %AbortJS("FAIL: expected <" + expected_breaks + "> breaks instead of <" +
                break_count + ">");
     }
     if (exception !== null) {
       %AbortJS("FAIL: exception: " + exception);
     }
   });
   dummy.foo = 1;
 }