[liveedit] fix stepping after replacing bytecode.

test/mjsunit/debug-liveedit-exceptions.js

+// Copyright 2016 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() {
+  throw 'Emacs';
+}
+
+var exception = null;
+var results = [];
+var log = []
+
+function listener(event, exec_state, event_data, data) {
+  if (event != Debug.DebugEvent.Exception) return;
+  try {
+    var source_line = event_data.sourceLineText();
+    print(source_line);
+    log.push(source_line);
+    switch (results.length) {
+      case 0:
+        Replace(BestEditor, "Emacs", "Eclipse");
+        break;
+      case 1:
+        Replace(BestEditor, "Eclipse", "Vim");
+        break;
+      case 2:
+        break;
+      default:
+        assertUnreachable();
+    }
+  } 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);
+Debug.setBreakOnException();
+
+for (var i = 0; i < 3; i++) {
+  try {
+    BestEditor();
+  } catch (e) {
+    results.push(e);
+  }
+}
+Debug.setListener(null);
+
+assertNull(exception);
+assertEquals(["Emacs", "Eclipse", "Vim"], results);
+print(JSON.stringify(log, 1));
+assertEquals([
+  "  throw 'Emacs';",
+  "  throw 'Eclipse';",
+  "  throw 'Vim';",
+], log);