Add check for file system access to the sandbox.

sandbox/linux/services/credentials.h

 // Copyright (c) 2013 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 SANDBOX_LINUX_SERVICES_CREDENTIALS_H_
 #define SANDBOX_LINUX_SERVICES_CREDENTIALS_H_
 
 #include "build/build_config.h"
 // Link errors are tedious to track, raise a compile-time error instead.
 #if defined(OS_ANDROID)
@@ skipping 76 matching lines @@
   // CAP_SYS_CHROOT can be acquired by using the MoveToNewUserNS() API.
   // |proc_fd| must be a file descriptor to /proc/ and must be the only open
   // directory file descriptor of the process.
   //
   // CRITICAL:
   //   - the caller must close |proc_fd| eventually or access to the file
   // system can be recovered.
   //   - DropAllCapabilities() must be called to prevent escapes.
   static bool DropFileSystemAccess(int proc_fd) WARN_UNUSED_RESULT;
 
+  // This function returns true if the process can still access the filesystem.
+  static bool HasFileSystemAccess();
+
   // Forks and drops capabilities in the child.
   static pid_t ForkAndDropCapabilitiesInChild();
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(Credentials);
 };
 
 }  // namespace sandbox.
 
 #endif  // SANDBOX_LINUX_SERVICES_CREDENTIALS_H_