Make it possible to set the display mode from Chromium

extensions/browser/app_window/app_window.cc

Index: extensions/browser/app_window/app_window.cc
diff --git a/extensions/browser/app_window/app_window.cc b/extensions/browser/app_window/app_window.cc
index 83f29714f43fc036ca6371e82a0fa4f2ebf2827e..b65d083a4bdb8695c3e38db0cb863b31d262e2f1 100644
--- a/extensions/browser/app_window/app_window.cc
+++ b/extensions/browser/app_window/app_window.cc
@@ -964,6 +964,13 @@ bool AppWindow::IsFullscreenForTabOrPending(const content::WebContents* source)
   return IsHtmlApiFullscreen();
 }
 
+blink::WebDisplayMode AppWindow::GetDisplayMode(
+    const content::WebContents* source) const {
+  if (IsFullscreen() && !IsHtmlApiFullscreen())
+    return blink::WebDisplayModeFullscreen;
+  return blink::WebDisplayModeStandalone;
+}
+
 void AppWindow::Observe(int type,
                         const content::NotificationSource& source,
                         const content::NotificationDetails& details) {