aura: Unify WindowTreeHost for some platforms

ui/platform_window/platform_window.h

Index: ui/platform_window/platform_window.h
diff --git a/ui/platform_window/platform_window.h b/ui/platform_window/platform_window.h
index a8fd6ee37fe49e33298142daac59b2cabb9254be..a46610c56a7ea0cd2d97203760ece16300b2a017 100644
--- a/ui/platform_window/platform_window.h
+++ b/ui/platform_window/platform_window.h
@@ -24,6 +24,8 @@ class PlatformWindowDelegate;
 // underlying platform windowing system (i.e. X11/Win/OSX).
 class PlatformWindow {
  public:
+  static scoped_ptr<PlatformWindow> Create(PlatformWindowDelegate* delegate,

[mfomitchev, 2015/10/08 15:03:27]

IMHO it's better just to do an ifdef in the constructor in  WindowTreeHostImpl.
There's a few problems with adding this method here. E.g. this is currently only
implemented for Windows and Ozone. We need this for other platforms if we are
going to do this. Also the new dependency on Ozone seems unfortunate.

[no sievers, 2015/10/09 00:34:18]

Done. For non-Ozone I left it with the implementation though, since ui_aura
doesn't really need to depend on that (i.e. window_android rather than just
platform_window).

[mfomitchev, 2015/10/09 13:56:54]

Do you mean just in the header files? The Aura module itself would still need to
depend on /ui/platform_window/android, since WTHPlatform would instantiate it on
Android, otherwise we'll get a linking error when building Aura for Android.
Just like Aura depends on /ui/platform_window/win... On this note, I also had to
make Aura depend on //ui/platform_window/android:platform_window_java to make it
run - see https://codereview.chromium.org/1391893003/

Also, if we are going to make that ifdef !defined(USE_OZONE), we need to
implement Create on other platforms (X11, etc). Personally I don't think it's
worth the hassle.

[no sievers, 2015/10/09 20:47:46]

Done.

+                                           const gfx::Rect& bounds);
   virtual ~PlatformWindow() {}
 
   virtual void Show() = 0;