Use the source display's pixel size as a mirror window's size.

ash/ash.gyp

Index: ash/ash.gyp
diff --git a/ash/ash.gyp b/ash/ash.gyp
index 91201540e4ada691dbba42a41cf0a6fd6df1ebe3..96e918c05c873f301de7706233d4f71f3923358a 100644
--- a/ash/ash.gyp
+++ b/ash/ash.gyp
@@ -64,8 +64,6 @@
         'accelerators/nested_dispatcher_controller.h',
         'ash_constants.cc',
         'ash_constants.h',
-        'ash_root_window_transformer.cc',
-        'ash_root_window_transformer.h',
         'ash_switches.cc',
         'ash_switches.h',
         'cancel_mode.cc',
@@ -105,6 +103,8 @@
         'display/mouse_cursor_event_filter.h',
         'display/output_configurator_animation.cc',
         'display/output_configurator_animation.h',
+        'display/root_window_transformers.cc',
+        'display/root_window_transformers.h',
         'display/screen_position_controller.cc',
         'display/screen_position_controller.h',
         'display/shared_display_edge_indicator.cc',
@@ -630,15 +630,15 @@
         'accelerators/accelerator_filter_unittest.cc',
         'accelerators/accelerator_table_unittest.cc',
         'accelerators/nested_dispatcher_controller_unittest.cc',
-        'ash_root_window_transformer_unittest.cc',
         'desktop_background/desktop_background_controller_unittest.cc',
         'dip_unittest.cc',
         'display/display_controller_unittest.cc',
         'display/display_error_dialog_unittest.cc',
         'display/display_info_unittest.cc',
+        'display/display_manager_unittest.cc',
         'display/mirror_window_controller_unittest.cc',
         'display/mouse_cursor_event_filter_unittest.cc',
-        'display/display_manager_unittest.cc',
+        'display/root_window_transformers_unittest.cc',
         'display/screen_position_controller_unittest.cc',
         'drag_drop/drag_drop_controller_unittest.cc',
         'drag_drop/drag_drop_tracker_unittest.cc',