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

components/offline_pages/core/recent_tabs/BUILD.gn

Index: components/offline_pages/core/recent_tabs/BUILD.gn
diff --git a/components/offline_pages/core/recent_tabs/BUILD.gn b/components/offline_pages/core/recent_tabs/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..fa8f938a665bf1661eb487eb144430d320e47556
--- /dev/null
+++ b/components/offline_pages/core/recent_tabs/BUILD.gn
@@ -0,0 +1,39 @@
+# 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",
+  ]
+}