Provide list of step-in source positions in JS Debug API

src/mirror-debugger.js

 // Copyright 2006-2012 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 1491 matching lines @@
     return this.details_[return_value_offset];
   }
 };
 
 
 FrameDetails.prototype.scopeCount = function() {
   return %GetScopeCount(this.break_id_, this.frameId());
 };
 
 
+FrameDetails.prototype.stepInPositionsImpl = function() {
+  return %GetStepInPositions(this.break_id_, this.frameId());
+};
+
+
 /**
  * Mirror object for stack frames.
  * @param {number} break_id The break id in the VM for which this frame is
        valid
  * @param {number} index The frame index (top frame is index 0)
  * @constructor
  * @extends Mirror
  */
 function FrameMirror(break_id, index) {
   %_CallFunction(this, FRAME_TYPE, Mirror);
@@ skipping 140 matching lines @@
 FrameMirror.prototype.scopeCount = function() {
   return this.details_.scopeCount();
 };
 
 
 FrameMirror.prototype.scope = function(index) {
   return new ScopeMirror(this, void 0, index);
 };
 
 
+FrameMirror.prototype.stepInPositions = function() {
+  var script = this.func().script();
+  var funcOffset = this.func().sourcePosition_();
+
+  var stepInRaw = this.details_.stepInPositionsImpl();
+  var result = [];
+  if (stepInRaw) {
+    for (var i = 0; i < stepInRaw.length; i++) {
+      var posStruct = {};
+      var offset = script.locationFromPosition(funcOffset + stepInRaw[i],
+                                               true);
+      serializeLocationFields(offset, posStruct);
+      var item = {
+        position: posStruct
+      };
+      result.push(item);
+    }
+  }
+
+  return result;
+};
+
+
 FrameMirror.prototype.evaluate = function(source, disable_break,
                                           opt_context_object) {
   var result = %DebugEvaluate(this.break_id_,
                               this.details_.frameId(),
                               this.details_.inlinedFrameIndex(),
                               source,
                               Boolean(disable_break),
                               opt_context_object);
   return MakeMirror(result);
 };
@@ skipping 935 matching lines @@
   }
   if (!NUMBER_IS_FINITE(value)) {
     if (value > 0) {
       return 'Infinity';
     } else {
       return '-Infinity';
     }
   }
   return value;
 }