ui: Add libsync GLFence implementation.

ui/gfx/shared_event.cc

Index: ui/gfx/shared_event.cc
diff --git a/ui/gfx/shared_event.cc b/ui/gfx/shared_event.cc
index b19d0329df127f934081e32bc2456e078f5aa9a4..396ad1a2929deabf3d593e9ccad92750ad1f9cae 100644
--- a/ui/gfx/shared_event.cc
+++ b/ui/gfx/shared_event.cc
@@ -48,6 +48,11 @@ SharedEventHandle SharedEvent::CreateForProcess(base::ProcessHandle process) {
 }
 
 // static
+bool SharedEvent::IsHandleValid(const SharedEventHandle& handle) {
+  return base::SharedMemory::IsHandleValid(handle);
+}
+
+// static
 SharedEventHandle SharedEvent::DuplicateHandle(
     const SharedEventHandle& handle) {
   return base::SharedMemory::DuplicateHandle(handle);