cros: Adds ShellPort functions for simplified display mode

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 2459aea36d6a5e46c70af7da6f2bb8d9bb21887c..d29ae7a561af83deea93ed3a867bd01b215d118f 100644
--- a/ash/host/ash_window_tree_host.h
+++ b/ash/host/ash_window_tree_host.h
@@ -31,7 +31,9 @@ class ASH_EXPORT AshWindowTreeHost {
   AshWindowTreeHost();
   virtual ~AshWindowTreeHost() {}
 
-  // Creates a new AshWindowTreeHost. The caller owns the returned value.
+  // Creates the appropriate AshWindowTreeHost implementation. The return
+  // value is owned by the RootWindowController associated with the
+  // AshWindowTreeHost.
   static AshWindowTreeHost* Create(

[James Cook, 2017/04/18 00:43:39]

It would be nice if this returned unique_ptr<>, even if the caller immediately
release()'d it.

[sky, 2017/04/18 02:55:10]

I actually had that in an earlier patch, but convinced myself ownership should
happen via the RootWindowController. But that doesn't matter here, so back to
making this return a unique_ptr.

       const AshWindowTreeHostInitParams& init_params);