Revert "[Wi-Fi] Apply WifiTrackerLib objects in Wi-Fi Slice"

This reverts commit 7b1aded2a6.

Reason for revert: Settings is crashing for WiFi selection in SetupWizard on wembley

Bug: 161434533
Change-Id: I1d90e9bae1b31862fba674db0d7497e43f987a7f
Test: Locally reverted, reflashed, and was able to select WiFi without Settings crashing.
Exempt-From-Owner-Approval: Revert to clear up P0 while all owners are outside of work hours

src/com/android/settings/wifi/slice/ContextualWifiScanWorker.java

@@ -18,6 +18,7 @@ package com.android.settings.wifi.slice;
 
 import android.content.Context;
 import android.net.Uri;
+import android.os.SystemClock;
 
 import com.android.settings.slices.SliceBackgroundWorker;
 
@@ -26,12 +27,44 @@ import com.android.settings.slices.SliceBackgroundWorker;
  */
 public class ContextualWifiScanWorker extends WifiScanWorker {
 
+    private static long sVisibleUiSessionToken;
+    private static long sActiveSession;
+
     public ContextualWifiScanWorker(Context context, Uri uri) {
         super(context, uri);
     }
 
+    /**
+     * Starts a new visible UI session for the purpose of automatically starting captive portal.
+     *
+     * A visible UI session is defined as a duration of time when a UI screen is visible to user.
+     * Going to a sub-page and coming out breaks the continuation, leaving the page and coming back
+     * breaks it too.
+     */
+    public static void newVisibleUiSession() {
+        sVisibleUiSessionToken = SystemClock.elapsedRealtime();
+    }
+
+    static void saveSession() {
+        sActiveSession = sVisibleUiSessionToken;
+    }
+
+    @Override
+    protected void clearClickedWifiOnSliceUnpinned() {
+        // Do nothing for contextual Wi-Fi slice
+    }
+
+    @Override
+    protected boolean isSessionValid() {
+        if (sVisibleUiSessionToken != sActiveSession) {
+            clearClickedWifi();
+            return false;
+        }
+        return true;
+    }
+
     @Override
     protected int getApRowCount() {
         return ContextualWifiSlice.getApRowCount();
     }
-}
+}