Add custom interstitial for captive portals.

chrome/browser/captive_portal/captive_portal_service.h

Index: chrome/browser/captive_portal/captive_portal_service.h
diff --git a/chrome/browser/captive_portal/captive_portal_service.h b/chrome/browser/captive_portal/captive_portal_service.h
index 66e6d1b4182049e14af547361a2e04522fe8148f..b15674577fb56432a5e670a350fff5d9976d51c7 100644
--- a/chrome/browser/captive_portal/captive_portal_service.h
+++ b/chrome/browser/captive_portal/captive_portal_service.h
@@ -30,8 +30,10 @@ class CaptivePortalService : public KeyedService, public base::NonThreadSafe {
   enum TestingState {
     NOT_TESTING,
     DISABLED_FOR_TESTING,  // The service is always disabled.
-    SKIP_OS_CHECK_FOR_TESTING  // The service can be enabled even if the OS has
+    SKIP_OS_CHECK_FOR_TESTING, // The service can be enabled even if the OS has
                                // native captive portal detection.
+    IGNORE_REQUESTS_FOR_TESTING  // Disables actual portal checks. This also
+                                 // implies SKIP_OS_CHECK_FOR_TESTING.
   };
 
   // The details sent via a NOTIFICATION_CAPTIVE_PORTAL_CHECK_RESULT.