services/ui: Inject GpuService instance where needed, instead of singleton.

ash/mus/window_manager_application.cc

Index: ash/mus/window_manager_application.cc
diff --git a/ash/mus/window_manager_application.cc b/ash/mus/window_manager_application.cc
index a24d0b6dbf99d92fd47b40d7b607e39a2c5fc40b..2bb259d27bcc286323390219e04d00e663f16676 100644
--- a/ash/mus/window_manager_application.cc
+++ b/ash/mus/window_manager_application.cc
@@ -96,7 +96,8 @@ void WindowManagerApplication::InitWindowManager(
 void WindowManagerApplication::OnStart(const shell::Identity& identity) {
   aura_init_.reset(new views::AuraInit(connector(), "ash_mus_resources.pak"));
   gpu_service_ = ui::GpuService::Initialize(connector());
-  compositor_context_factory_.reset(new views::SurfaceContextFactory());
+  compositor_context_factory_.reset(
+      new views::SurfaceContextFactory(gpu_service_.get()));
   aura::Env::GetInstance()->set_context_factory(
       compositor_context_factory_.get());
   window_manager_.reset(new WindowManager(connector()));