Revert of Add support for ContentViewCore helpers on Tab

chrome/android/java/src/org/chromium/chrome/browser/EmptyTabObserver.java

 // Copyright 2013 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;
 
 import android.view.ContextMenu;
 
-import org.chromium.content.browser.ContentViewCore;
 import org.chromium.content_public.browser.WebContents;
 
 /**
  * An implementation of the {@link TabObserver} which has empty implementations of all methods.
  */
 public class EmptyTabObserver implements TabObserver {
 
     @Override
     public void onShown(Tab tab) { }
 
     @Override
     public void onHidden(Tab tab) { }
 
     @Override
     public void onClosingStateChanged(Tab tab, boolean closing) { }
 
     @Override
     public void onDestroyed(Tab tab) { }
 
     @Override
     public void onContentChanged(Tab tab) { }
 
     @Override
-    public void onOverlayContentViewCoreAdded(Tab tab, ContentViewCore content) { }
-
-    @Override
-    public void onOverlayContentViewCoreRemoved(Tab tab, ContentViewCore content) { }
-
-    @Override
     public void onLoadUrl(Tab tab, String url, int loadType) { }
 
     @Override
     public void onPageLoadStarted(Tab tab) { }
 
     @Override
     public void onPageLoadFinished(Tab tab) { }
 
     @Override
     public void onPageLoadFailed(Tab tab, int errorCode) { }
@@ skipping 69 matching lines @@
     @Override
     public void onDidStartNavigationToPendingEntry(Tab tab, String url) { }
 
     @Override
     public void onBackgroundColorChanged(Tab tab, int color) { }
 
     @Override
     public void webContentsCreated(Tab tab, WebContents sourceWebContents, long openerRenderFrameId,
             String frameName, String targetUrl, WebContents newWebContents) { }
 }