mus: Split the gpu client-lib into a separate component.

ui/views/mus/mus_client.h

Index: ui/views/mus/mus_client.h
diff --git a/ui/views/mus/mus_client.h b/ui/views/mus/mus_client.h
index f19685c90e775ef0b2733d9fe8b0bd20c3f39d04..38087cd9e7815e036d03f56023832850e54a30e0 100644
--- a/ui/views/mus/mus_client.h
+++ b/ui/views/mus/mus_client.h
@@ -15,7 +15,6 @@
 #include "ui/views/widget/widget.h"
 
 namespace aura {
-class GpuService;
 class PropertyConverter;
 class MusContextFactory;
 class Window;
@@ -31,6 +30,10 @@ class Connector;
 class Identity;
 }
 
+namespace ui {
+class GpuService;
+}
+
 namespace wm {
 class WMState;
 }
@@ -119,7 +122,7 @@ class VIEWS_MUS_EXPORT MusClient
 
   std::unique_ptr<aura::WindowTreeClient> window_tree_client_;
 
-  std::unique_ptr<aura::GpuService> gpu_service_;
+  std::unique_ptr<ui::GpuService> gpu_service_;
 
   std::unique_ptr<aura::MusContextFactory> compositor_context_factory_;