Reject filesystem root entries as args for chrome.fileSystem functions.

chrome/browser/extensions/api/file_handlers/app_file_handler_util.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/extensions/api/file_handlers/app_file_handler_util.h"
 
 #include "base/file_util.h"
 #include "base/files/file_path.h"
 #include "chrome/browser/extensions/extension_prefs.h"
 #include "content/public/browser/browser_thread.h"
@@ skipping 332 matching lines @@
 bool HasFileSystemWritePermission(const Extension* extension) {
   return extension->HasAPIPermission(APIPermission::kFileSystemWrite);
 }
 
 bool ValidateFileEntryAndGetPath(
     const std::string& filesystem_name,
     const std::string& filesystem_path,
     const content::RenderViewHost* render_view_host,
     base::FilePath* file_path,
     std::string* error) {
+  if (filesystem_path.empty()) {
+    *error = kInvalidParameters;
+    return false;
+  }
+
   std::string filesystem_id;
   if (!fileapi::CrackIsolatedFileSystemName(filesystem_name, &filesystem_id)) {
     *error = kInvalidParameters;
     return false;
   }
 
   // Only return the display path if the process has read access to the
   // filesystem.
   content::ChildProcessSecurityPolicy* policy =
       content::ChildProcessSecurityPolicy::GetInstance();
@@ skipping 24 matching lines @@
     *error = kInvalidParameters;
     return false;
   }
 
   return true;
 }
 
 }  // namespace app_file_handler_util
 
 }  // namespace extensions