Only show Last N Pages in the UI when the corresponding tab is visible.

chrome/browser/android/offline_pages/downloads/offline_page_download_bridge.cc

 // 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.
 
 #include "chrome/browser/android/offline_pages/downloads/offline_page_download_bridge.h"
 
 #include <vector>
 
 #include "base/android/jni_string.h"
 #include "base/bind.h"
@@ skipping 40 matching lines @@
 
 namespace {
 
 class DownloadUIAdapterDelegate : public DownloadUIAdapter::Delegate {
  public:
   explicit DownloadUIAdapterDelegate(OfflinePageModel* model);
 
   // DownloadUIAdapter::Delegate
   bool IsVisibleInUI(const ClientId& client_id) override;
   bool IsTemporarilyHiddenInUI(const ClientId& client_id) override;
+  void SetUIAdapter(DownloadUIAdapter* ui_adapter) override;
 
  private:
   // Not owned, cached service pointer.
   OfflinePageModel* model_;
 };
 
 DownloadUIAdapterDelegate::DownloadUIAdapterDelegate(OfflinePageModel* model)
     : model_(model) {}
 
 bool DownloadUIAdapterDelegate::IsVisibleInUI(const ClientId& client_id) {
   const std::string& name_space = client_id.name_space;
   return model_->GetPolicyController()->IsSupportedByDownload(name_space) &&
          base::IsValidGUID(client_id.id);
 }
 
 bool DownloadUIAdapterDelegate::IsTemporarilyHiddenInUI(
     const ClientId& client_id) {
   return false;
 }
 
+void DownloadUIAdapterDelegate::SetUIAdapter(DownloadUIAdapter* ui_adapter) {}
+
 // TODO(dewittj): Move to Download UI Adapter.
 content::WebContents* GetWebContentsFromJavaTab(
     const ScopedJavaGlobalRef<jobject>& j_tab_ref) {
   JNIEnv* env = AttachCurrentThread();
   TabAndroid* tab = TabAndroid::GetNativeTab(env, j_tab_ref);
   if (!tab)
     return nullptr;
 
   return tab->web_contents();
 }
@@ skipping 397 matching lines @@
         base::MakeUnique<DownloadUIAdapterDelegate>(offline_page_model));
     offline_page_model->SetUserData(kDownloadUIAdapterKey, adapter);
   }
 
   return reinterpret_cast<jlong>(
       new OfflinePageDownloadBridge(env, obj, adapter, browser_context));
 }
 
 }  // namespace android
 }  // namespace offline_pages