Debugger: PreservePositionScope should clear positions inside the scope.

test/mjsunit/regress/regress-crbug-481896.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
+
+function static() {
+  print("> static");  // Break
+}
+
+var Debug = debug.Debug;
+var exception = null;
+var break_count = 0;
+
+function listener(event, exec_state, event_data, data) {
+  if (event != Debug.DebugEvent.Break) return;
+  try {
+    print("breakpoint hit at " + exec_state.frame(0).sourceLineText());
+    assertTrue(exec_state.frame(0).sourceLineText().indexOf("// Break") > 0);
+    break_count++;
+  } catch (e) {
+    exception = e;
+  }
+}
+
+Debug.setListener(listener);
+
+function install() {
+  eval("this.dynamic = function dynamic() { \n" +
+       "  print(\"> dynamic\");  // Break\n" +
+       "}\n" +
+       "//@ sourceURL=dynamicScript");
+}
+
+install();
+
+var scripts = Debug.scripts();
+var dynamic_script;
+var static_script;
+for (var script of scripts) {
+  if (script.source_url == "dynamicScript") dynamic_script = script;
+  if (script.source_url == "staticScript") static_script = script;
+}
+
+Debug.setScriptBreakPointById(dynamic_script.id, 1);
+Debug.setScriptBreakPointById(static_script.id, 7);
+
+dynamic();
+static();
+
+Debug.setListener(null);
+
+assertNull(exception);
+assertEquals(2, break_count);
+
+//@ sourceURL=staticScript