Add custom interstitial for captive portals.

chrome/browser/captive_portal/captive_portal_service.cc

Index: chrome/browser/captive_portal/captive_portal_service.cc
diff --git a/chrome/browser/captive_portal/captive_portal_service.cc b/chrome/browser/captive_portal/captive_portal_service.cc
index 93c37a8c1b81f69c8f9c174e934e7a1276f8a3bd..26248862a6cfb05da801d7dc5b518260f7630b62 100644
--- a/chrome/browser/captive_portal/captive_portal_service.cc
+++ b/chrome/browser/captive_portal/captive_portal_service.cc
@@ -214,6 +214,10 @@ CaptivePortalService::~CaptivePortalService() {
 void CaptivePortalService::DetectCaptivePortal() {
   DCHECK(CalledOnValidThread());
 
+  // Detection should be disabled only in tests.
+  if (testing_state_ == IGNORE_REQUESTS_FOR_TESTING)
+    return;
+
   // If a request is pending or running, do nothing.
   if (state_ == STATE_CHECKING_FOR_PORTAL || state_ == STATE_TIMER_RUNNING)
     return;