Add the notification for actively prefer bad wifi

With this patch and "config_activelyPreferBadWifi=1"
(or SDK level >= U) and bad wifi avoidance turned off,
when the device connects to a bad wifi, after 20
seconds of the wifi not validating the device will
pop up a head-up notification with text
"<SSID> has no internet access".

When tapped, the notification will bring up the existing
Settings dialog :
*Wifi not connected to the internet*
You can switch to mobile whenever Wi-Fi is bad
 □ Never show again
 <Stay on Wi-Fi> <Switch to Mobile>

If the wifi validates and loses access again, the same
notification/dialog are shown if Settings.Global.
NETWORK_AVOID_BAD_WIFI=PROMPT ; if IGNORE, the device
stays stuck on wifi.
If AVOID, then bad wifi avoidance is turned on in the
first place, so none of this happens.

Behavior in other cases :
- If config_activelyPreferBadWifi=0, then upon connecting
  to a wifi without internet, the behavior is unchanged :
  the device stays on mobile and after 8 seconds a
  notification pops up asking whether to stay connected.
  If the network validates, then loses access, the behavior
  depends on a few things :
  - If config_networkAvoidBadWifi is 0 and Settings.Global.
    NETWORK_AVOID_BAD_WIFI = IGNORE, then the device stays
    on wifi and says nothing.
  - If config_networkAvoidBadWifi is 0 and Settings.Global.
    NETWORK_AVOID_BAD_WIFI = PROMPT, then
    notification pops up asking whether to switch to mobile.
  - If config_networkAvoidBadWifi is 1 (regardless of the
    value of Settings.Global.NETWORK_AVOID_BAD_WIFI), or if
    Settings.Global.NETWORK_AVOID_BAD_WIFI = AVOID, then
    the device switches back to mobile.

- If Mobile is not connected, all the above applies. This
  is not great for the messages including "switch to mobile"
  but this patch doesn't change it.

Test: manual
Change-Id: Idb05b6a6e5c085f5ef72435d462e14bfd1341f87

service/src/com/android/server/ConnectivityService.java

@@ -5238,6 +5238,16 @@ public class ConnectivityService extends IConnectivityManager.Stub
             // network was found not to have Internet access.
             nai.updateScoreForNetworkAgentUpdate();
             rematchAllNetworksAndRequests();
+
+            // Also, if this is WiFi and it should be preferred actively, now is the time to
+            // prompt the user that they walked past and connected to a bad WiFi.
+            if (nai.networkCapabilities.hasTransport(TRANSPORT_WIFI)
+                    && !avoidBadWifi()
+                    && activelyPreferBadWifi()) {
+                // The notification will be removed if the network validates or disconnects.
+                showNetworkNotification(nai, NotificationType.LOST_INTERNET);
+                return;
+            }
         }
 
         if (!shouldPromptUnvalidated(nai)) return;