aura: Some change to how the client-lib is set up.

ui/aura/mus/window_tree_client.h

Index: ui/aura/mus/window_tree_client.h
diff --git a/ui/aura/mus/window_tree_client.h b/ui/aura/mus/window_tree_client.h
index 7c89cf1f89eca617cde6eb5e2c34f930ef5399ea..dbfd0867e48687b2204d4b33ee999a09757cdbec 100644
--- a/ui/aura/mus/window_tree_client.h
+++ b/ui/aura/mus/window_tree_client.h
@@ -42,6 +42,10 @@ namespace service_manager {
 class Connector;
 }
 
+namespace ui {
+class Gpu;
+}
+
 namespace aura {
 class CaptureSynchronizer;
 class DragDropControllerMus;
@@ -51,6 +55,7 @@ class InFlightChange;
 class InFlightFocusChange;
 class InFlightPropertyChange;
 class InFlightVisibleChange;
+class MusContextFactory;
 class WindowMus;
 class WindowPortMus;
 struct WindowPortPropertyData;
@@ -85,6 +90,7 @@ class AURA_EXPORT WindowTreeClient
  public:
   explicit WindowTreeClient(
       service_manager::Connector* connector,
+      scoped_refptr<base::SingleThreadTaskRunner> io_task_runner,

[sadrul, 2017/01/19 20:15:22]

An alternative is to introduce an InitializeGpu(io_task_runner), which sets up
|gpu_| and |compositor_context_factory_|. Let me know if you prefer that, over
adding this in the ctor.

[sky, 2017/01/19 21:52:58]

I'm ok with what you have, but WDYT of moving io_task_runner to the end of the
list with a default value of null? I suggest this as it seems as though null is
used in most (all?) cases.

[sadrul, 2017/01/20 06:20:32]

Makes sense. Done. (MusClient is the only place that sends the task-runner)

       WindowTreeClientDelegate* delegate,
       WindowManagerDelegate* window_manager_delegate = nullptr,
       ui::mojom::WindowTreeClientRequest request = nullptr);
@@ -97,6 +103,7 @@ class AURA_EXPORT WindowTreeClient
   void ConnectAsWindowManager();
 
   service_manager::Connector* connector() { return connector_; }
+  ui::Gpu* gpu() { return gpu_.get(); }
 
   bool connected() const { return tree_ != nullptr; }
   ClientSpecificId client_id() const { return client_id_; }
@@ -523,6 +530,8 @@ class AURA_EXPORT WindowTreeClient
 
   std::unique_ptr<DragDropControllerMus> drag_drop_controller_;
 
+  std::unique_ptr<ui::Gpu> gpu_;
+  std::unique_ptr<MusContextFactory> compositor_context_factory_;
   base::WeakPtrFactory<WindowTreeClient> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowTreeClient);