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

components/offline_pages/core/recent_tabs/BUILD.gn

+# 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.
+
+if (is_android) {
+  import("//build/config/android/rules.gni")
+}
+
+source_set("recent_tabs") {
+  sources = [
+    "recent_tabs_ui_adapter_delegate.cc",
+    "recent_tabs_ui_adapter_delegate.h",
+  ]
+
+  deps = [
+    "//base",
+    "//components/offline_pages/core",
+    "//components/offline_pages/core/downloads:offline_pages_ui_adapter",
+    "//url",
+  ]
+}
+
+source_set("unit_tests") {
+  testonly = true
+  sources = [
+    "recent_tabs_ui_adapter_delegate_unittest.cc",
+  ]
+
+  deps = [
+    ":recent_tabs",
+    "//base",
+    "//base/test:test_support",
+    "//components/offline_pages/core",
+    "//components/offline_pages/core:test_support",
+    "//components/offline_pages/core/background:test_support",
+    "//components/offline_pages/core/downloads:offline_pages_ui_adapter",
+    "//testing/gtest",
+  ]
+}