Use mojo SystemTray interfaces for both mash and classic ash

ash/common/mojo_interface_factory.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 ASH_COMMON_MOJO_INTERFACE_FACTORY_H_
+#define ASH_COMMON_MOJO_INTERFACE_FACTORY_H_
+
+#include "ash/ash_export.h"
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+
+namespace base {
+class SingleThreadTaskRunner;
+}
+
+namespace shell {
+class InterfaceRegistry;
+}
+
+namespace ash {
+
+class ASH_EXPORT MojoInterfaceFactory {

[Ken Rockot(use gerrit already), 2016/10/03 18:19:03]

optional nit: Style guide says don't introduce classes which only have static
methods, but to instead just use namespaced functions. I personally don't see
the value of that rule, but you could optionally move this to something like
ash::RegisterMojoInterfaces.

[James Cook, 2016/10/03 20:15:00]

Changed to use namespaced functions.

+ public:
+  // Registers all mojo services provided by ash. May be called on IO thread
+  // (when running ash in-process in chrome) or on the main thread (when running
+  // in mash).
+  static void RegisterInterfaces(
+      shell::InterfaceRegistry* registry,
+      scoped_refptr<base::SingleThreadTaskRunner> main_thread_task_runner);
+
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(MojoInterfaceFactory);
+};
+
+}  // namespace ash
+
+#endif  // ASH_COMMON_MOJO_INTERFACE_FACTORY_H_