Update from https://crrev.com/316786

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)
 #error "Android is not supported."
 #endif  // defined(OS_ANDROID).
 
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
 #include "sandbox/sandbox_export.h"
 
 namespace sandbox {
 
 // This class should be used to manipulate the current process' credentials.
 // It is currently a stub used to manipulate POSIX.1e capabilities as
 // implemented by the Linux kernel.
 class SANDBOX_EXPORT Credentials {
  public:
   // Drop all capabilities in the effective, inheritable and permitted sets for
-  // the current process.
+  // the current process. For security reasons, since capabilities are
+  // per-thread, the caller is responsible for ensuring it is single-threaded
+  // when calling this API.
   static bool DropAllCapabilities() WARN_UNUSED_RESULT;
   // Return true iff there is any capability in any of the capabilities sets
   // of the current process.
   static bool HasAnyCapability();
   // Returns the capabilities of the current process in textual form, as
   // documented in libcap2's cap_to_text(3). This is mostly useful for
   // debugging and tests.
   static scoped_ptr<std::string> GetCurrentCapString();
 
   // Returns whether the kernel supports CLONE_NEWUSER and whether it would be
@@ skipping 24 matching lines @@
   // that file descriptor). Otherwise it may be possible to escape the chroot.
   static bool DropFileSystemAccess() WARN_UNUSED_RESULT;
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(Credentials);
 };
 
 }  // namespace sandbox.
 
 #endif  // SANDBOX_LINUX_SERVICES_CREDENTIALS_H_