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

apps/custom_launcher_page_contents.cc

Index: apps/custom_launcher_page_contents.cc
diff --git a/apps/custom_launcher_page_contents.cc b/apps/custom_launcher_page_contents.cc
index 8888993aac5c39e380dc2df0ecc7ff1d34ae93ab..f1738a34c8380e50a09a1caa0203a74138f4774a 100644
--- a/apps/custom_launcher_page_contents.cc
+++ b/apps/custom_launcher_page_contents.cc
@@ -11,6 +11,7 @@
 #include "content/public/browser/render_view_host.h"
 #include "content/public/browser/site_instance.h"
 #include "content/public/browser/web_contents.h"
+#include "content/public/browser/web_contents_source.h"
 #include "content/public/common/renderer_preferences.h"
 #include "extensions/browser/app_window/app_delegate.h"
 #include "extensions/browser/app_window/app_web_contents_helper.h"
@@ -34,6 +35,8 @@ void CustomLauncherPageContents::Initialize(content::BrowserContext* context,
       content::WebContents::Create(content::WebContents::CreateParams(
           context, content::SiteInstance::CreateForURL(context, url))));
 
+  WebContentsSource::CreateForWebContentsAndLocation(web_contents_.get(),
+                                                     FROM_HERE);
   web_contents_->GetMutableRendererPrefs()
       ->browser_handles_all_top_level_requests = true;
   web_contents_->GetRenderViewHost()->SyncRendererPrefs();