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

ui/aura/mus/mus_context_factory.h

Index: ui/aura/mus/mus_context_factory.h
diff --git a/ui/aura/mus/mus_context_factory.h b/ui/aura/mus/mus_context_factory.h
index 1ec518d233c56ee48d272814ff0f05e2cf4fd106..14ed82e48bf9b6c1424f29b91f2d41213536fcfa 100644
--- a/ui/aura/mus/mus_context_factory.h
+++ b/ui/aura/mus/mus_context_factory.h
@@ -14,13 +14,16 @@
 #include "ui/aura/aura_export.h"
 #include "ui/compositor/compositor.h"
 
-namespace aura {
+namespace ui {
 class GpuService;
+}
+
+namespace aura {
 
 // ContextFactory implementation that can be used with Mus.
 class AURA_EXPORT MusContextFactory : public ui::ContextFactory {
  public:
-  explicit MusContextFactory(GpuService* gpu_service);
+  explicit MusContextFactory(ui::GpuService* gpu_service);
   ~MusContextFactory() override;
 
  private:
@@ -57,7 +60,7 @@ class AURA_EXPORT MusContextFactory : public ui::ContextFactory {
   cc::SurfaceManager surface_manager_;
   uint32_t next_sink_id_;
   ui::RasterThreadHelper raster_thread_helper_;
-  GpuService* gpu_service_;
+  ui::GpuService* gpu_service_;
 
   DISALLOW_COPY_AND_ASSIGN(MusContextFactory);
 };