📰 Add visibility change triggers for bottom sheet content

chrome/android/java/src/org/chromium/chrome/browser/widget/bottomsheet/EmptyBottomSheetObserver.java

 // Copyright 2017 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.widget.bottomsheet;
 
 import org.chromium.chrome.browser.widget.bottomsheet.BottomSheet.BottomSheetContent;
 
 /**
  * An empty base implementation of the {@link BottomSheetObserver} interface.
@@ skipping 15 matching lines @@
     public void onSheetOffsetChanged(float heightFraction) {}
 
     @Override
     public void onTransitionPeekToHalf(float transitionFraction) {}
 
     @Override
     public void onSheetStateChanged(int newState) {}
 
     @Override
     public void onSheetContentChanged(BottomSheetContent newContent) {}
+
+    @Override
+    public void onSheetBackgrounded() {}
+
+    @Override
+    public void onSheetForegrounded() {}
 }