Add initial BUILD.gn in platform/wtf/, and move first a few files there.

third_party/WebKit/Source/wtf/CryptographicallyRandomNumber.h

-/*
- * Copyright (C) 2008 Torch Mobile Inc. All rights reserved.
- * (http://www.torchmobile.com/)
- *
- * 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
- *    documentation and/or other materials provided with the distribution.
- *
- * THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
- * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
- * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
- * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
- * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
- * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
- * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
- * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
- * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
- * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
- * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
- */
+// Copyright 2017 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 WTF_CryptographicallyRandomNumber_h
-#define WTF_CryptographicallyRandomNumber_h
+#include "platform/wtf/CryptographicallyRandomNumber.h"
 
-#include "wtf/WTFExport.h"
-#include <cstddef>
-#include <stdint.h>
-
-namespace WTF {
-
-WTF_EXPORT void setAlwaysZeroRandomSourceForTesting();
-
-// These functions are threadsafe.
-WTF_EXPORT uint32_t cryptographicallyRandomNumber();
-WTF_EXPORT void cryptographicallyRandomValues(void* buffer, size_t length);
-}
-
-using WTF::cryptographicallyRandomNumber;
-using WTF::cryptographicallyRandomValues;
-
-#endif
+// The contents of this header was moved to platform/wtf as part of
+// WTF migration project. See the following post for details:
+// https://groups.google.com/a/chromium.org/d/msg/blink-dev/tLdAZCTlcAA/bYXVT8gYCAAJ