Revert of [inspector] migrate stepping related methods to debug-interface

src/inspector/debugger_script_externs.js

Index: src/inspector/debugger_script_externs.js
diff --git a/src/inspector/debugger_script_externs.js b/src/inspector/debugger_script_externs.js
index daaf8c6b24796f01e98c6b71efba50378a63b10b..88a52360d23e051df41ccba6f7d32603a8f795a4 100644
--- a/src/inspector/debugger_script_externs.js
+++ b/src/inspector/debugger_script_externs.js
@@ -61,6 +61,8 @@
  */
 var Debug = {};
 
+Debug.clearStepping = function() {}
+
 Debug.clearAllBreakPoints = function() {}
 
 /** @return {!Array<!Script>} */
@@ -189,6 +191,9 @@
 
 /** @interface */
 function ExecutionState() {}
+
+/** @param {!Debug.StepAction} action */
+ExecutionState.prototype.prepareStep = function(action) {}
 
 /**
  * @param {string} source