Actually enable tab persistence for CCTs.

chrome/android/java/src/org/chromium/chrome/browser/customtabs/SeparateTaskManagedCustomTabActivity.java

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.chrome.browser.customtabs;
 
 import android.content.Intent;
 import android.os.SystemClock;
 
 import org.chromium.chrome.browser.IntentHandler.IntentHandlerDelegate;
@@ skipping 70 matching lines @@
     private int getActivityIndex() {
         // Cull out the activity index from the class name.
         String baseClassName = SeparateTaskCustomTabActivity.class.getSimpleName();
         String className = this.getClass().getSimpleName();
         assert className.matches("^" + baseClassName + "[0-9]+$");
         String indexString = className.substring(baseClassName.length());
         return Integer.parseInt(indexString);
     }
 
     @Override
-    public void finishAndClose() {
+    protected void handleFinishAndClose() {
         Intent intent = new Intent(getIntent());
         intent.setFlags(intent.getFlags() & ~Intent.FLAG_ACTIVITY_NEW_TASK);
         intent.addFlags(Intent.FLAG_ACTIVITY_EXCLUDE_FROM_RECENTS);
         intent.putExtra(FORCE_FINISH, true);
         startActivity(intent);
     }
 }