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

components/constrained_window/constrained_window_views.cc

Index: components/constrained_window/constrained_window_views.cc
diff --git a/components/constrained_window/constrained_window_views.cc b/components/constrained_window/constrained_window_views.cc
index 5ae6cd7776da6ae7eb24433ddda5d07c808fa9bd..3bf1dfc386b7974af9295047db567239d677f841 100644
--- a/components/constrained_window/constrained_window_views.cc
+++ b/components/constrained_window/constrained_window_views.cc
@@ -6,6 +6,7 @@
 
 #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"
@@ -146,6 +147,12 @@ views::Widget* ShowWebModalDialogViews(
 
 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,