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

third_party/WebKit/Source/wtf/WTFExport.h

Index: third_party/WebKit/Source/wtf/WTFExport.h
diff --git a/third_party/WebKit/Source/wtf/WTFExport.h b/third_party/WebKit/Source/wtf/WTFExport.h
index ba1005f9305d5eb97bd3f05340b07565106e6dfd..9e313a571da0381db0865adb6df73ffa86f1f679 100644
--- a/third_party/WebKit/Source/wtf/WTFExport.h
+++ b/third_party/WebKit/Source/wtf/WTFExport.h
@@ -1,52 +1,9 @@
-/*
- * 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:
- *
- *     * Redistributions of source code must retain the above copyright
- * notice, this list of conditions and the following disclaimer.
- *     * 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.
- *     * Neither the name of Google Inc. nor the names of its
- * contributors may be used to endorse or promote products derived from
- * this software without specific prior written permission.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * "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 THE COPYRIGHT
- * OWNER 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 WTFExport_h
-#define WTFExport_h
+#include "platform/wtf/WTFExport.h"
 
-#if !defined(WTF_IMPLEMENTATION)
-#define WTF_IMPLEMENTATION 0
-#endif
-
-#if defined(COMPONENT_BUILD)
-#if defined(WIN32)
-#if WTF_IMPLEMENTATION
-#define WTF_EXPORT __declspec(dllexport)
-#else
-#define WTF_EXPORT __declspec(dllimport)
-#endif
-#else  // defined(WIN32)
-#define WTF_EXPORT __attribute__((visibility("default")))
-#endif
-#else  // defined(COMPONENT_BUILD)
-#define WTF_EXPORT
-#endif
-
-#endif  // WTFExport_h
+// 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