Add an 'allow-top-navigation-with-user-interaction' sandbox flag.

third_party/WebKit/Source/core/dom/SandboxFlags.h

 /*
  * Copyright (C) 2013 Google Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 37 matching lines @@
   SandboxPointerLock = 1 << 8,
   SandboxDocumentDomain = 1 << 9,
   // See
   // https://w3c.github.io/screen-orientation/#dfn-sandboxed-orientation-lock-browsing-context-flag.
   SandboxOrientationLock = 1 << 10,
   SandboxPropagatesToAuxiliaryBrowsingContexts = 1 << 11,
   SandboxModals = 1 << 12,
   // See
   // https://w3c.github.io/presentation-api/#sandboxing-and-the-allow-presentation-keyword
   SandboxPresentation = 1 << 13,
+  // See https://github.com/WICG/interventions/issues/42.
+  SandboxTopNavigationWithUserActivation = 1 << 14,
   SandboxAll = -1  // Mask with all bits set to 1.
 };
 
 typedef int SandboxFlags;
 
 SandboxFlags parseSandboxPolicy(const SpaceSplitString& policy,
                                 String& invalidTokensErrorMessage);
 
 }  // namespace blink
 
 #endif