ui: Add libsync GLFence implementation.

ui/gl/gl_fence_libsync.h

+// Copyright 2016 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 UI_GL_GL_FENCE_LIBSYNC_H_
+#define UI_GL_GL_FENCE_LIBSYNC_H_
+
+#include "base/file_descriptor_posix.h"
+#include "base/files/scoped_file.h"
+#include "base/macros.h"
+#include "ui/gl/gl_export.h"
+#include "ui/gl/gl_fence.h"
+
+namespace gl {
+
+class GL_EXPORT GLFenceLibsync : public GLFence {
+ public:
+  explicit GLFenceLibsync(base::ScopedFD fd);
+  ~GLFenceLibsync() override;
+
+  // Overridden from GLFence:
+  bool HasCompleted() override;
+  void ClientWait() override;
+  void ServerWait() override;
+
+ private:
+  base::ScopedFD fd_;
+
+  DISALLOW_COPY_AND_ASSIGN(GLFenceLibsync);
+};
+
+}  // namespace gl
+
+#endif  // UI_GL_GL_FENCE_LIBSYNC_H_