Revert of 📺 Move fullscreen web content to a new Activity.

chrome/android/java/src/org/chromium/chrome/browser/tabmodel/SingleTabModel.java

 // Copyright 2015 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.tabmodel;
 
 import android.app.Activity;
 
 import org.chromium.base.ActivityState;
 import org.chromium.base.ApiCompatibilityUtils;
 import org.chromium.base.ApplicationStatus;
 import org.chromium.base.ObserverList;
 import org.chromium.chrome.browser.profiles.Profile;
 import org.chromium.chrome.browser.tab.Tab;
 
 /**
  * Simple TabModel that assumes that only one Tab exists.
  */
 public class SingleTabModel implements TabModel {
     private final Activity mActivity;
-    private final ObserverList<TabModelObserver> mObservers = new ObserverList<>();
+    private final ObserverList<TabModelObserver> mObservers = new ObserverList<TabModelObserver>();
 
     private Tab mTab;
     private boolean mIsIncognito;
     private boolean mBlockNewWindows;
 
     SingleTabModel(Activity activity, boolean incognito, boolean blockNewWindows) {
         mActivity = activity;
         mIsIncognito = incognito;
         mBlockNewWindows = blockNewWindows;
     }
@@ skipping 134 matching lines @@
     public boolean supportsPendingClosures() {
         return false;
     }
 
     @Override
     public void addTab(Tab tab, int index, TabLaunchType type) {
     }
 
     @Override
     public void removeTab(Tab tab) {
-        mTab = null;
-        for (TabModelObserver obs : mObservers) obs.tabRemoved(tab);
+        assert false;
     }
 
     @Override
     public void addObserver(TabModelObserver observer) {
         mObservers.addObserver(observer);
     }
 
     @Override
     public void removeObserver(TabModelObserver observer) {
         mObservers.removeObserver(observer);
     }
 
     private static native void nativePermanentlyBlockAllNewWindows(Tab nativeTabAndroid);
 
     @Override
     public void openMostRecentlyClosedTab() {
     }
 
 }