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

ash/display/mirror_window_controller.h

Index: ash/display/mirror_window_controller.h
diff --git a/ash/display/mirror_window_controller.h b/ash/display/mirror_window_controller.h
index e7b96c78613da4caf3dbaea1afa1070443b113fa..aa99553ad12713f7e809fbfb57f36209270deabb 100644
--- a/ash/display/mirror_window_controller.h
+++ b/ash/display/mirror_window_controller.h
@@ -8,6 +8,7 @@
 #include "ash/ash_export.h"
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
+#include "ui/aura/window_observer.h"

[James Cook, 2013/05/29 12:22:43]

Do you need this here?

[oshima, 2013/05/29 15:39:49]

Done.

 #include "ui/gfx/native_widget_types.h"
 #include "ui/gfx/point.h"
 
@@ -37,6 +38,11 @@ class MirrorWindowController {
   // Creates the new root window if one doesn't exist.
   void UpdateWindow(const DisplayInfo& display_info);
 
+  // Same as above, but using existing display info
+  // for the mirrored display.
+  void UpdateWindow();
+
+  // Close the mirror window.
   void Close();
 
   // Updates the mirrored cursor location,shape and