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

chrome/android/java/src/org/chromium/chrome/browser/dom_distiller/ReaderModeManager.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.dom_distiller;
 
 import android.content.Context;
 import android.text.TextUtils;
 
 import org.chromium.base.CommandLine;
@@ skipping 138 matching lines @@
                 mIsFindToolbarShowing = false;
                 requestReaderPanelShow(StateChangeReason.UNKNOWN);
             }
         };
     }
 
     // TabModelSelectorTabObserver:
 
     @Override
     public void onShown(Tab shownTab) {
-        if (mTabModelSelector == null) return;
-
         int shownTabId = shownTab.getId();
         Tab previousTab = mTabModelSelector.getTabById(mTabId);
         mTabId = shownTabId;
 
         // If the reader panel was dismissed, stop here.
         if (mTabStatusMap.containsKey(shownTabId)
                 && mTabStatusMap.get(shownTabId).isDismissed()) {
             return;
         }
 
@@ skipping 472 matching lines @@
 
         boolean enabled = CommandLine.getInstance().hasSwitch(ChromeSwitches.ENABLE_DOM_DISTILLER)
                 && !CommandLine.getInstance().hasSwitch(
                         ChromeSwitches.DISABLE_READER_MODE_BOTTOM_BAR)
                 && !DeviceFormFactor.isTablet(context)
                 && DomDistillerTabUtils.isDistillerHeuristicsEnabled()
                 && !SysUtils.isLowEndDevice();
         return enabled;
     }
 }