Add custom interstitial for captive portals.

chrome/browser/captive_portal/captive_portal_tab_helper.h

Index: chrome/browser/captive_portal/captive_portal_tab_helper.h
diff --git a/chrome/browser/captive_portal/captive_portal_tab_helper.h b/chrome/browser/captive_portal/captive_portal_tab_helper.h
index 421afcd8efab82ef75f48016825c1925d931ba06..d6b6a8993a4469a6ea65e77ef6048593806002a8 100644
--- a/chrome/browser/captive_portal/captive_portal_tab_helper.h
+++ b/chrome/browser/captive_portal/captive_portal_tab_helper.h
@@ -108,6 +108,10 @@ class CaptivePortalTabHelper
   // page.  This is set to false when a captive portal is no longer detected.
   bool IsLoginTab() const;
 
+  // Opens a login tab if the profile's active window doesn't have one already.
+  static void OpenLoginTabForWebContents(content::WebContents* web_contents,
+                                         bool focus);
+
  private:
   friend class CaptivePortalBrowserTest;
   friend class CaptivePortalTabHelperTest;
@@ -140,9 +144,6 @@ class CaptivePortalTabHelper
 
   CaptivePortalTabReloader* GetTabReloaderForTest();
 
-  // Opens a login tab if the profile's active window doesn't have one already.
-  void OpenLoginTab();
-
   Profile* profile_;
 
   // Neither of these will ever be NULL.