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 a4ec27454df92b5b1e65c900942a4e3c2812afba..3b425c4631d11ee1de0124ab802b0c43af8ce7b9 100644
--- a/chrome/browser/ui/panels/panel_host.cc
+++ b/chrome/browser/ui/panels/panel_host.cc
@@ -11,6 +11,7 @@
 #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"
@@ -53,14 +54,16 @@ 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 {