[debugger] fix liveedit in combination with step in.

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";
+  return best_editor;
+}
+
+var exception = null;
+var results = [];
+var log = []
+
+function listener(event, exec_state, event_data, data) {
+  if (event != Debug.DebugEvent.Break) return;
+  try {
+    var source_line = event_data.sourceLineText();
+    log.push(source_line);
+    if (source_line.indexOf("return") >= 0) {
+      switch (results.length) {
+        case 0:
+          break;
+        case 1:
+          Replace(BestEditor, "Emacs", "Eclipse");
+          break;
+        case 2:
+          Replace(BestEditor, "Eclipse", "Vim");
+          break;
+        default:
+          assertUnreachable();
+      }
+    }
+    exec_state.prepareStep(Debug.StepAction.StepIn, 1);
+  } 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 = [];
+  Debug.LiveEdit.TestApi.ApplySingleChunkPatch(script, patch_pos, original.length, patch, change_log);
+}
+
+Debug.setListener(listener);
+
+debugger;
+results.push(BestEditor());
+results.push(BestEditor());
+results.push(BestEditor());
+Debug.setListener(null);
+
+assertNull(exception);
+assertEquals(["Emacs", "Eclipse", "Vim"], results);
+print(JSON.stringify(log, 1));
+assertEquals([
+  "debugger;",
+  "results.push(BestEditor());",
+  "  var best_editor = \"Emacs\";",
+  "  return best_editor;","}",
+  "results.push(BestEditor());",
+  "results.push(BestEditor());",
+  "  var best_editor = \"Emacs\";",
+  "  return best_editor;",
+  "  var best_editor = \"Eclipse\";",
+  "  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);