Keep the module in scope when executing scripts. This prevents a crash when the

ppapi/proxy/ppb_var_deprecated_proxy.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ppapi/proxy/ppb_var_deprecated_proxy.h"
 
 #include <stdlib.h>  // For malloc
 
 #include "base/logging.h"
 #include "ppapi/c/dev/ppb_var_deprecated.h"
@@ skipping 297 matching lines @@
     &var_deprecated_interface,
     PPB_VAR_DEPRECATED_INTERFACE,
     INTERFACE_ID_PPB_VAR_DEPRECATED,
     false,
     &CreateVarDeprecatedProxy,
   };
   return &info;
 }
 
 bool PPB_Var_Deprecated_Proxy::OnMessageReceived(const IPC::Message& msg) {
+  // Prevent the dispatcher from going away during a call to Call or other
+  // function that could mutate the DOM. This must happen OUTSIDE of
+  // the message handlers since the SerializedVars use the dispatcher upon
+  // return of the function (converting the SerializedVarReturnValue/OutParam
+  // to a SerializedVar in the destructor).
+  ScopedModuleReference death_grip(dispatcher());
+
   bool handled = true;
   IPC_BEGIN_MESSAGE_MAP(PPB_Var_Deprecated_Proxy, msg)
     IPC_MESSAGE_HANDLER(PpapiHostMsg_PPBVar_HasProperty,
                         OnMsgHasProperty)
     IPC_MESSAGE_HANDLER(PpapiHostMsg_PPBVar_HasMethodDeprecated,
                         OnMsgHasMethodDeprecated)
     IPC_MESSAGE_HANDLER(PpapiHostMsg_PPBVar_GetProperty,
                         OnMsgGetProperty)
     IPC_MESSAGE_HANDLER(PpapiHostMsg_PPBVar_DeleteProperty,
                         OnMsgDeleteProperty)
@@ skipping 135 matching lines @@
 
 void PPB_Var_Deprecated_Proxy::SetAllowPluginReentrancy() {
   if (dispatcher()->IsPlugin())
     NOTREACHED();
   else
     static_cast<HostDispatcher*>(dispatcher())->set_allow_plugin_reentrancy();
 }
 
 }  // namespace proxy
 }  // namespace pp