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

chrome/browser/ui/panels/panel_host.cc

Index: chrome/browser/ui/panels/panel_host.cc
diff --git a/chrome/browser/ui/panels/panel_host.cc b/chrome/browser/ui/panels/panel_host.cc
index 5de546f073e1a95c555c9487f16222cb34ed1101..18b0d3803a3e248522e22550788db06fb848841b 100644
--- a/chrome/browser/ui/panels/panel_host.cc
+++ b/chrome/browser/ui/panels/panel_host.cc
@@ -30,6 +30,7 @@
 #include "content/public/browser/site_instance.h"
 #include "content/public/browser/user_metrics.h"
 #include "content/public/browser/web_contents.h"
+#include "content/public/browser/web_contents_source.h"
 #include "extensions/browser/view_type_utils.h"
 #include "ipc/ipc_message.h"
 #include "ipc/ipc_message_macros.h"
@@ -54,6 +55,8 @@ void PanelHost::Init(const GURL& url) {
   content::WebContents::CreateParams create_params(
       profile_, content::SiteInstance::CreateForURL(profile_, url));
   web_contents_.reset(content::WebContents::Create(create_params));
+  WebContentsSource::CreateForWebContentsAndLocation(web_contents_.get(),
+                                                     FROM_HERE);
   extensions::SetViewType(web_contents_.get(), extensions::VIEW_TYPE_PANEL);
   web_contents_->SetDelegate(this);
   // web_contents_ may be passed to PageZoom::Zoom(), so it needs