Move native_app_window code to apps areas

apps/shell_window.h

Index: apps/shell_window.h
diff --git a/apps/shell_window.h b/apps/shell_window.h
index a10cb5bd553337afb52b60d27ab109006401a03d..6bf4ebfe53e4c8362d77b1a70f8ae446b891f528 100644
--- a/apps/shell_window.h
+++ b/apps/shell_window.h
@@ -21,7 +21,6 @@
 
 class GURL;
 class Profile;
-class NativeAppWindow;
 class SkRegion;
 
 namespace content {
@@ -42,6 +41,8 @@ class BaseWindow;
 
 namespace apps {
 
+class NativeAppWindow;
+
 // Manages the web contents for Shell Windows. The implementation for this
 // class should create and maintain the WebContents for the window, and handle
 // any message passing between the web contents and the extension system or
@@ -130,6 +131,9 @@ class ShellWindow : public content::NotificationObserver,
 
     // General initialization.
     virtual void InitWebContents(content::WebContents* web_contents) = 0;
+    virtual NativeAppWindow* CreateNativeAppWindow(
+        ShellWindow* window,
+        const CreateParams& params) = 0;
 
     // Link handling.
     virtual content::WebContents* OpenURLFromTab(