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

chrome/browser/android/offline_pages/offline_page_utils.h

 // Copyright 2015 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.
 
 #ifndef CHROME_BROWSER_ANDROID_OFFLINE_PAGES_OFFLINE_PAGE_UTILS_H_
 #define CHROME_BROWSER_ANDROID_OFFLINE_PAGES_OFFLINE_PAGE_UTILS_H_
 
 #include <stdint.h>
 
 #include "base/callback.h"
@@ skipping 91 matching lines @@
                                       const GURL& url,
                                       const DuplicateCheckCallback& callback);
 
   // Schedules to download a page from |url| and categorize under |name_space|.
   // The duplicate pages or requests will be checked. Note that |url| can be
   // different from the one rendered in |web_contents|.
   static void ScheduleDownload(content::WebContents* web_contents,
                                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
 
 #endif  // CHROME_BROWSER_ANDROID_OFFLINE_PAGES_OFFLINE_PAGE_UTILS_H_