ash: Add RootWindowHostFactory class.

ash/ash.gyp

Index: ash/ash.gyp
diff --git a/ash/ash.gyp b/ash/ash.gyp
index 6f3d16b98676ca572b1057cae0dda8afbc553c7b..1720494bcaf53fe2db967678ae44128c6c92a4de 100644
--- a/ash/ash.gyp
+++ b/ash/ash.gyp
@@ -100,6 +100,9 @@
         'focus_cycler.h',
         'high_contrast/high_contrast_controller.cc',
         'high_contrast/high_contrast_controller.h',
+        'host/root_window_host_factory.cc',
+        'host/root_window_host_factory.h',
+        'host/root_window_host_factory_win.cc',
         'keyboard_overlay/keyboard_overlay_delegate.cc',
         'keyboard_overlay/keyboard_overlay_delegate.h',
         'keyboard_overlay/keyboard_overlay_view.cc',
@@ -439,6 +442,11 @@
             ['exclude', 'accelerators/nested_dispatcher_controller.h'],
           ],
         }],
+        ['OS=="win"', {
+          'sources/': [
+            ['exclude', 'host/root_window_host_factory.cc'],
+          ],
+        }],
         ['OS!="linux"', {
           'sources/': [
             ['exclude', 'system/monitor/tray_monitor.cc'],