ui: Add libsync GLFence implementation.

ui/gl/gl_fence_libsync.cc

+// 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.
+
+#include "ui/gl/gl_fence_libsync.h"
+
+#include "base/trace_event/trace_event.h"
+#include "third_party/libsync/include/sync/sync.h"
+
+namespace gl {
+
+GLFenceLibsync::GLFenceLibsync(base::ScopedFD fd) : fd_(std::move(fd)) {}
+
+GLFenceLibsync::~GLFenceLibsync() {}
+
+bool GLFenceLibsync::HasCompleted() {
+  int rv = sync_wait(fd_.get(), 0);
+  PLOG_IF(ERROR, rv < 0) << "sync_wait failed: " << rv;
+  return !rv;
+}
+
+void GLFenceLibsync::ClientWait() {
+  TRACE_EVENT0("gpu", "GLFenceLibsync::ClientWait");
+  int rv = sync_wait(fd_.get(), -1);
+  PLOG_IF(ERROR, rv < 0) << "sync_wait failed: " << rv;
+}
+
+void GLFenceLibsync::ServerWait() {
+  ClientWait();
+}
+
+}  // namespace gl