gpu: Add GpuFence framework.

ui/gl/gl_fence_shared_event.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_shared_event.h"
+
+namespace gl {
+
+GLFenceSharedEvent::GLFenceSharedEvent(const gfx::SharedEventHandle& handle)
+    : shared_event_(handle) {
+  // Close shared memory segment to avoid running out of FDs.
+  shared_event_.Close();

[ericrk, 2017/03/10 03:04:39]

So, to make sure I understand, closing this frees up an FD, but does not unmap
the memory (or break the link that mapped memory has to other procs)?

[reveman, 2017/03/13 12:33:05]

Correct. We do the same for shared bitmaps and discardable memory when possible
for the same reason.

+}
+
+GLFenceSharedEvent::~GLFenceSharedEvent() {}
+
+bool GLFenceSharedEvent::HasCompleted() {
+  return shared_event_.IsSignaled();
+}
+
+void GLFenceSharedEvent::ClientWait() {
+  DLOG(WARNING) << "Unsupported fence operation";
+}
+
+void GLFenceSharedEvent::ServerWait() {
+  DLOG(WARNING) << "Unsupported fence operation";
+}
+
+bool GLFenceSharedEvent::SignalSupported() {
+  return true;
+}
+
+void GLFenceSharedEvent::Signal() {
+  shared_event_.Signal();
+}
+
+}  // namespace gl