Use DownloadManager to download non-html res when download icon pressed

chrome/browser/android/offline_pages/offline_page_utils.h

Index: chrome/browser/android/offline_pages/offline_page_utils.h
diff --git a/chrome/browser/android/offline_pages/offline_page_utils.h b/chrome/browser/android/offline_pages/offline_page_utils.h
index 7a4c3b7dddf64620adcea2b767a051b241b7933c..f539f9369b54e00dd91a3ac3b010ecc440dcc744 100644
--- a/chrome/browser/android/offline_pages/offline_page_utils.h
+++ b/chrome/browser/android/offline_pages/offline_page_utils.h
@@ -109,6 +109,11 @@ class OfflinePageUtils {
                                const std::string& name_space,
                                const GURL& url,
                                DownloadUIActionFlags ui_action);
+
+  // Determines if offline page download should be triggered based on MIME type
+  // of download resource.
+  static bool CanDownloadAsOfflinePage(const GURL& url,
+                                       const std::string& contents_mime_type);
 };
 
 }  // namespace offline_pages