mash: Provide a fake chromeos StatisticsProvider in ash

ash/mus/window_manager_application.h

Index: ash/mus/window_manager_application.h
diff --git a/ash/mus/window_manager_application.h b/ash/mus/window_manager_application.h
index 1259e052e64d3f631785e56310ff4aa7c3b609c6..84477455955b4e47baaf01f93465996c8117eef0 100644
--- a/ash/mus/window_manager_application.h
+++ b/ash/mus/window_manager_application.h
@@ -20,6 +20,12 @@
 #include "services/ui/common/types.h"
 #include "services/ui/public/interfaces/accelerator_registrar.mojom.h"
 
+namespace chromeos {
+namespace system {
+class ScopedFakeStatisticsProvider;
+}
+}
+
 namespace views {
 class AuraInit;
 class SurfaceContextFactory;
@@ -95,6 +101,11 @@ class WindowManagerApplication
   mojo::Binding<mash::session::mojom::ScreenlockStateListener>
       screenlock_state_listener_binding_;
 
+#if defined(OS_CHROMEOS)
+  std::unique_ptr<chromeos::system::ScopedFakeStatisticsProvider>
+      statistics_provider_;
+#endif
+
   DISALLOW_COPY_AND_ASSIGN(WindowManagerApplication);
 };