[exp] ash: sysui for mash

ash/host/ash_window_tree_host.h

Index: ash/host/ash_window_tree_host.h
diff --git a/ash/host/ash_window_tree_host.h b/ash/host/ash_window_tree_host.h
index 54724aa5fcf9224d43fdba04e571375d7ff004b0..f53c18480c2ae299dfcfdcca73e6602ca3270203 100644
--- a/ash/host/ash_window_tree_host.h
+++ b/ash/host/ash_window_tree_host.h
@@ -6,6 +6,7 @@
 #define ASH_HOST_ASH_WINDOW_TREE_HOST_H_
 
 #include "ash/ash_export.h"
+#include "base/callback_forward.h"
 #include "base/memory/scoped_ptr.h"
 
 namespace aura {
@@ -31,12 +32,16 @@ class RootWindowTransformer;
 
 class ASH_EXPORT AshWindowTreeHost {
  public:
+  using Factory =
+      base::Callback<AshWindowTreeHost*(const AshWindowTreeHostInitParams&)>;
+
   AshWindowTreeHost();
   virtual ~AshWindowTreeHost() {}
 
   // Creates a new AshWindowTreeHost. The caller owns the returned value.
   static AshWindowTreeHost* Create(
       const AshWindowTreeHostInitParams& init_params);
+  static void SetFactory(const Factory& factory);

[sky, 2016/02/03 22:43:48]

This seems ick. Can't we create the create the right one directly when in mus?

[sadrul, 2016/02/04 00:03:42]

We cannot create the right one directly from the mus-app; the AshWindowTreeHost
gets created a few steps deep inside of the call to Shell::CreateInstance():

  ash::AshWindowTreeHost::Create()
  ash::WindowTreeHostManager::AddWindowTreeHostForDisplay()
  ash::WindowTreeHostManager::CreatePrimaryHost()                               

  ash::Shell::Init()
  ash::Shell::CreateInstance()

To create the right one directly from AshWindowTreeHost::Create() would require
the mus-bits to be built into the ash component itself, and I want to avoid
having to do that. Another option would be to introduce
AshWindowTreeHostInitParams::Factory. (although I think it's simpler as it is
now, and it's somewhat similar to
Env::set_context_factory/ViewsDelegate::set_native_widget_factory etc.)

 
   void set_input_method_handler(InputMethodEventHandler* input_method_handler) {
     input_method_handler_ = input_method_handler;