Add enable-offlining-recent-pages feature switch.

components/offline_pages/offline_page_feature.h

Index: components/offline_pages/offline_page_feature.h
diff --git a/components/offline_pages/offline_page_feature.h b/components/offline_pages/offline_page_feature.h
index 600140ff2cffbcc6f47ef4a4dd8bf15d5b7fd18f..1d01a2d495ca35640c9e0cc0b17e3281d87a078a 100644
--- a/components/offline_pages/offline_page_feature.h
+++ b/components/offline_pages/offline_page_feature.h
@@ -5,12 +5,13 @@
 #ifndef COMPONENTS_OFFLINE_PAGES_OFFLINE_PAGE_FEATURE_H_
 #define COMPONENTS_OFFLINE_PAGES_OFFLINE_PAGE_FEATURE_H_
 
+#include "base/feature_list.h"
 #include "build/build_config.h"
 
-#if defined(OS_ANDROID)
-
 namespace offline_pages {
 
+extern const base::Feature kOffliningRecentPagesFeature;
+
 // GENERATED_JAVA_ENUM_PACKAGE: org.chromium.components.offlinepages
 enum class FeatureMode {
   // Offline pages feature is disabled.
@@ -27,8 +28,9 @@ FeatureMode GetOfflinePageFeatureMode();
 // Returns true if offline pages is enabled.
 bool IsOfflinePagesEnabled();
 
-}  // namespace offline_pages
+// Returns true if offlining of recent pages (aka 'Last N pages') is enabled.
+bool IsOffliningRecentPagesEnabled();
 
-#endif  // defined(OS_ANDROID)
+}  // namespace offline_pages
 
 #endif  // COMPONENTS_OFFLINE_PAGES_OFFLINE_PAGE_FEATURE_H_