Panels refactor: Support browserless panels on Linux.

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 9162967105b747a85534a3077b9a3292764428f3..e9d6f1aab0782c20a10746d49f94f062db0b1201 100644
--- a/chrome/browser/ui/panels/panel_host.cc
+++ b/chrome/browser/ui/panels/panel_host.cc
@@ -10,6 +10,7 @@
 #include "chrome/browser/favicon/favicon_tab_helper.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/panels/panel.h"
+#include "chrome/browser/ui/prefs/prefs_tab_helper.h"
 #include "chrome/browser/view_type_utils.h"
 #include "chrome/common/chrome_notification_types.h"
 #include "chrome/common/extensions/extension_messages.h"
@@ -51,14 +52,16 @@ void PanelHost::Init(const GURL& url) {
   content::WebContentsObserver::Observe(web_contents_.get());
 
   favicon_tab_helper_.reset(new FaviconTabHelper(web_contents_.get()));
+  prefs_tab_helper_.reset(new PrefsTabHelper(web_contents_.get()));
 
   web_contents_->GetController().LoadURL(
       url, content::Referrer(), content::PAGE_TRANSITION_LINK, std::string());
 }
 
 void PanelHost::DestroyWebContents() {
-  web_contents_.reset();
   favicon_tab_helper_.reset();
+  prefs_tab_helper_.reset();
+  web_contents_.reset();
 }
 
 SkBitmap PanelHost::GetPageIcon() const {