Add FilePath::FinalExtension() to avoid double extensions (.tar.gz) for file selector

chrome/browser/download/download_file_picker.cc

 // Copyright (c) 2012 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.
 
 #include "chrome/browser/download/download_file_picker.h"
 
 #include "base/metrics/histogram.h"
 #include "chrome/browser/download/download_prefs.h"
 #include "chrome/browser/platform_util.h"
 #include "chrome/browser/ui/chrome_select_file_policy.h"
@@ skipping 51 matching lines @@
   const DownloadPrefs* prefs =
       DownloadPrefs::FromBrowserContext(item->GetBrowserContext());
   DCHECK(prefs);
   // Only record UMA if we aren't prompting the user for all downloads.
   should_record_file_picker_result_ = !prefs->PromptForDownload();
 
   WebContents* web_contents = item->GetWebContents();
   select_file_dialog_ = ui::SelectFileDialog::Create(
       this, new ChromeSelectFilePolicy(web_contents));
   ui::SelectFileDialog::FileTypeInfo file_type_info;
-  base::FilePath::StringType extension = suggested_path_.Extension();
+  // Platform file pickers, notably on Mac and Windows, tend to break
+  // with double extensions like .tar.gz, so only pass in normal ones.
+  base::FilePath::StringType extension = suggested_path_.FinalExtension();
   if (!extension.empty()) {
     extension.erase(extension.begin());  // drop the .
     file_type_info.extensions.resize(1);
     file_type_info.extensions[0].push_back(extension);
   }
   file_type_info.include_all_files = true;
   file_type_info.support_drive = true;
   gfx::NativeWindow owning_window = web_contents ?
       platform_util::GetTopLevel(web_contents->GetView()->GetNativeView()) :
       NULL;
@@ skipping 30 matching lines @@
   // Deletes |this|
 }
 
 // static
 void DownloadFilePicker::ShowFilePicker(DownloadItem* item,
                                         const base::FilePath& suggested_path,
                                         const FileSelectedCallback& callback) {
   new DownloadFilePicker(item, suggested_path, callback);
   // DownloadFilePicker deletes itself.
 }