Fix crash with print preview and the new scrollbar code that triggered an assert in WebKit side. ...

webkit/plugins/ppapi/ppb_scrollbar_impl.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 "webkit/plugins/ppapi/ppb_scrollbar_impl.h"
 
 #include "base/logging.h"
 #include "base/message_loop.h"
 #include "ppapi/c/dev/ppp_scrollbar_dev.h"
 #include "ppapi/thunk/thunk.h"
@@ skipping 99 matching lines @@
 // static
 PP_Resource PPB_Scrollbar_Impl::Create(PluginInstance* instance,
                                        bool vertical) {
   scoped_refptr<PPB_Scrollbar_Impl> scrollbar(
       new PPB_Scrollbar_Impl(instance));
   scrollbar->Init(vertical);
   return scrollbar->GetReference();
 }
 
 PPB_Scrollbar_Impl::PPB_Scrollbar_Impl(PluginInstance* instance)
-    : PPB_Widget_Impl(instance) {
+    : PPB_Widget_Impl(instance),
+      ALLOW_THIS_IN_INITIALIZER_LIST(method_factory_(this)) {
 }
 
 PPB_Scrollbar_Impl::~PPB_Scrollbar_Impl() {
 }
 
 void PPB_Scrollbar_Impl::Init(bool vertical) {
 #if defined(WEBSCROLLBAR_SUPPORTS_OVERLAY)
   scrollbar_.reset(WebScrollbar::createForPlugin(
       vertical ? WebScrollbar::Vertical : WebScrollbar::Horizontal,
       instance()->container(),
@@ skipping 144 matching lines @@
     WebKit::WebScrollbar* scrollbar,
     const WebKit::WebRect& rect) {
   gfx::Rect gfx_rect(rect.x,
                      rect.y,
                      rect.width,
                      rect.height);
   dirty_ = dirty_.Union(gfx_rect);
   // Can't call into the client to tell them about the invalidate right away,
   // since the PPB_Scrollbar_Impl code is still in the middle of updating its
   // internal state.
+  // Note: we use a method factory here instead of NewRunnableMethod because the
+  // latter would modify the lifetime of this object. That might make
+  // WebKit::WebScrollbar outlive WebKit::WebPluginContainer, which is against
+  // its contract.
   MessageLoop::current()->PostTask(
       FROM_HERE,
-      NewRunnableMethod(this, &PPB_Scrollbar_Impl::NotifyInvalidate));
+      method_factory_.NewRunnableMethod(&PPB_Scrollbar_Impl::NotifyInvalidate));
 }
 
 void PPB_Scrollbar_Impl::getTickmarks(
     WebKit::WebScrollbar* scrollbar,
     WebKit::WebVector<WebKit::WebRect>* tick_marks) const {
   if (tickmarks_.empty()) {
     WebRect* rects = NULL;
     tick_marks->assign(rects, 0);
   } else {
     tick_marks->assign(&tickmarks_[0], tickmarks_.size());
   }
 }
 
 void PPB_Scrollbar_Impl::NotifyInvalidate() {
   if (dirty_.IsEmpty())
     return;
   PP_Rect pp_rect;
   pp_rect.point.x = dirty_.x();
   pp_rect.point.y = dirty_.y();
   pp_rect.size.width = dirty_.width();
   pp_rect.size.height = dirty_.height();
   dirty_ = gfx::Rect();
   Invalidate(&pp_rect);
 }
 
 }  // namespace ppapi
 }  // namespace webkit