third_party/WebKit/Source/platform/PluginScriptForbiddenScope.h

   1 // Copyright 2015 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef PluginScriptForbiddenScope_h
   6 #define PluginScriptForbiddenScope_h
   7
   8 #include "platform/PlatformExport.h"
   9
  10 namespace blink {
  11
  12 // Similar to ScriptForbiddenScope, but more selective. This is intended to help
  13 // reduce the number of places where Flash can run a nested message loop as its
  14 // plugin element is being destroyed. One of the reasons that Flash runs this
  15 // nested message loop is to allow Flash content to synchronously script the
  16 // page when the plugin element is destroyed.
  17 //
  18 // This is problematic for many reasons: the DOM may not be in a consistent
  19 // state, since Blink is in the middle of detaching nodes, nested message loops
  20 // can cause normally impossible conditions to occur (https://crbug.com/367210),
  21 // etc.
  22 //
  23 // When this object is instantiated on the stack, it allows execution of event
  24 // handlers, etc but blocks attempts by plugins to call back into Blink to
  25 // execute script.
  26 //
  27 // Background:
  28 // For historical reasons, Flash has allowed synchronous scripting during
  29 // teardown of the plugin. This is generally problematic, but sites apparently
  30 // rely on this behavior. Over time, Blink has added restrictions on this
  31 // synchronous scripting: for example, past a certain point in Frame detach,
  32 // script execution by Flash is ignored: https://crbug.com/371084.
  33 //
  34 // Unfortunately, there are still ways for plugins to synchronously script
  35 // during Document detach: if an unload handler removes a Flash plugin element,
  36 // that will run the nested message loop, etc. This scoper is intended to block
  37 // those usages, with the eventual goal that Frame detach will never have to run
  38 // a nested message loop.
  39 class PLATFORM_EXPORT PluginScriptForbiddenScope {
  40 public:
  41     PluginScriptForbiddenScope();
  42     ~PluginScriptForbiddenScope();
  43
  44     static bool isForbidden();
  45 };
  46
  47 } // namespace blink
  48
  49 #endif // PluginScriptForbiddenScope_h