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

content/browser/web_contents/web_contents_impl.cc

Index: content/browser/web_contents/web_contents_impl.cc
diff --git a/content/browser/web_contents/web_contents_impl.cc b/content/browser/web_contents/web_contents_impl.cc
index 6fe002a2866429580061c6b05694cd87a691d045..66c5003394e184ad1c579d03c1bc7fae5b774efd 100644
--- a/content/browser/web_contents/web_contents_impl.cc
+++ b/content/browser/web_contents/web_contents_impl.cc
@@ -2883,6 +2883,10 @@ void WebContentsImpl::ResumeLoadingCreatedWebContents() {
   }
 }
 
+base::debug::StackTrace WebContentsImpl::stack_trace() {
+  return stack_trace_;
+}
+
 bool WebContentsImpl::FocusLocationBarByDefault() {
   NavigationEntry* entry = controller_.GetVisibleEntry();
   if (entry && entry->GetURL() == GURL(url::kAboutBlankURL))