WIP: Plumbing input event latency reporting through Mus GPU.

ui/latency/latency_info_test_support.cc

Index: ui/latency/latency_info_test_support.cc
diff --git a/ui/latency/latency_info_test_support.cc b/ui/latency/latency_info_test_support.cc
new file mode 100644
index 0000000000000000000000000000000000000000..10fe183174f70b024164044c7b758dc26e16adc0
--- /dev/null
+++ b/ui/latency/latency_info_test_support.cc
@@ -0,0 +1,13 @@
+// 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.
+
+#include "ui/latency/latency_info.h"
+
+namespace ui {
+
+void PrintTo(const LatencyInfo& latency, ::std::ostream* os) {
+  *os << "LatencyInfo: trace_id=" << latency.trace_id();
+}
+
+}  // namespace ui