ash: Add RootWindowHostFactory class.

ui/aura/root_window.h

Index: ui/aura/root_window.h
diff --git a/ui/aura/root_window.h b/ui/aura/root_window.h
index 06755667fb240b3e255fba9dde1abe87ac2d72df..399779504c05f2941fa74b24076e36368e28ca4f 100644
--- a/ui/aura/root_window.h
+++ b/ui/aura/root_window.h
@@ -48,6 +48,7 @@ class ViewProp;
 namespace aura {
 
 class RootWindow;
+class RootWindowDelegate;
 class RootWindowHost;
 class RootWindowObserver;
 
@@ -68,9 +69,10 @@ class AURA_EXPORT RootWindow : public ui::CompositorDelegate,
 
     gfx::Rect initial_bounds;
 
-    // A host to use in place of the default one that RootWindow will create.
+    // RootWindow delegate. Can be used to create a host to use in place of the
+    // default one that RootWindow will create.
     // NULL by default.
-    RootWindowHost* host;
+    RootWindowDelegate* delegate;

[Ben Goodger (Google), 2012/12/11 01:14:02]

Why can't you just set host to the value you want?

This breaks desktop aura btw, which sets this field to something else in several
places in the code.

As an aside, I'd really like to see aura not have any of the RootWindowHost
impls. It's turned out that all of them are very implementation specific.

A very basic RootWindowHost interface should live in aura (much more simple than
what's there now), and nothing more. Ash would create its own kind, and
views/desktop-aura/chrome another.

[reveman, 2012/12/11 07:23:30]

OK, I like this. We don't need RootWindowDelegate. That was really just so we
could implement this cleanly without having an ash specific RootWindowHost.

Knowing that we want to move RootWindowHost impls to ash this patch can be made
simpler.

   };
 
   explicit RootWindow(const CreateParams& params);
@@ -351,6 +353,8 @@ class AURA_EXPORT RootWindow : public ui::CompositorDelegate,
   // current mouse location.
   void SynthesizeMouseMoveEvent();
 
+  scoped_ptr<RootWindowDelegate> delegate_;
+
   scoped_ptr<ui::Compositor> compositor_;
 
   scoped_ptr<RootWindowHost> host_;