Expose API to detect when captive portal probe was blocked on Android

net/android/network_library.h

Index: net/android/network_library.h
diff --git a/net/android/network_library.h b/net/android/network_library.h
index 24610bb50d2b4c3649d49fe15bee3cb730a8155d..548d43a1f2524457cbd3600639e52a5a4225cc72 100644
--- a/net/android/network_library.h
+++ b/net/android/network_library.h
@@ -71,6 +71,14 @@ NET_EXPORT std::string GetTelephonySimOperator();
 // true, it suggests that use of data may incur extra costs.
 NET_EXPORT bool GetIsRoaming();
 
+// Returns true if the system's captive portal probe was blocked for the current
+// default data network. The method will return false if the captive portal
+// probe was not blocked, the login process to the captive portal has been
+// successfully completed, or if the captive portal status can't be determined.
+// Requires ACCESS_NETWORK_STATE permission. Only available on Android
+// Marshmallow and later versions. Returns false on earlier versions.
+NET_EXPORT bool GetIsCaptivePortal();
+
 // Gets the SSID of the currently associated WiFi access point if there is one.
 // Otherwise, returns empty string.
 NET_EXPORT_PRIVATE std::string GetWifiSSID();