Track where WebContents are created in order to better understand issue.

components/constrained_window/constrained_window_views.cc

 // Copyright (c) 2012 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 "components/constrained_window/constrained_window_views.h"
 
 #include <algorithm>
 
+#include "base/debug/alias.h"
 #include "components/constrained_window/constrained_window_views_client.h"
 #include "components/guest_view/browser/guest_view_base.h"
 #include "components/web_modal/web_contents_modal_dialog_host.h"
 #include "components/web_modal/web_contents_modal_dialog_manager.h"
 #include "components/web_modal/web_contents_modal_dialog_manager_delegate.h"
 #include "ui/views/border.h"
 #include "ui/views/widget/widget.h"
 #include "ui/views/widget/widget_observer.h"
 #include "ui/views/window/dialog_delegate.h"
 
@@ skipping 120 matching lines @@
   content::WebContents* web_contents =
       guest_view::GuestViewBase::GetTopLevelWebContents(initiator_web_contents);
   views::Widget* widget = CreateWebModalDialogViews(dialog, web_contents);
   web_modal::WebContentsModalDialogManager::FromWebContents(web_contents)
       ->ShowModalDialog(widget->GetNativeWindow());
   return widget;
 }
 
 views::Widget* CreateWebModalDialogViews(views::WidgetDelegate* dialog,
                                          content::WebContents* web_contents) {
+  // Temporary to track down http://crbug.com/538612
+  content::WebContentsDelegate* delegate = web_contents->GetDelegate();
+  base::debug::Alias(delegate);

[Mike Wittman, 2015/11/17 16:24:06]

Have you verified that the vtable is captured in the crash dump with this
technique?

Can you get to the WebContentsDelegate pointer in any of the existing crash
dumps? If so, you may already be able to look at the vtables.

[ncarter (slow), 2015/11/17 17:42:16]

This should work; I wouldn't sweat it. For example, in the existing dumps you
could see the vtable of |web_contents|, which is just another local variable
captured by the dump.

[hcarmona, 2015/11/20 03:36:50]

I wasn't able to see the variable in the new crash dumps in VS :-(

delegate  -  Variable is optimized away and not available.
go/vuehm

+  CHECK(
+      web_modal::WebContentsModalDialogManager::FromWebContents(web_contents));
+
   DCHECK_EQ(ui::MODAL_TYPE_CHILD, dialog->GetModalType());
   return views::DialogDelegate::CreateDialogWidget(
       dialog, nullptr,
       web_modal::WebContentsModalDialogManager::FromWebContents(web_contents)
           ->delegate()
           ->GetWebContentsModalDialogHost()
           ->GetHostView());
 }
 
 views::Widget* CreateBrowserModalDialogViews(views::DialogDelegate* dialog,
@@ skipping 25 matching lines @@
     DCHECK_EQ(parent_view, host->GetHostView());
     ModalDialogHostObserver* dialog_host_observer =
         new WidgetModalDialogHostObserverViews(
             host, widget, kWidgetModalDialogHostObserverViewsKey);
     dialog_host_observer->OnPositionRequiresUpdate();
   }
   return widget;
 }
 
 }  // namespace constrained window