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 fc56bae8beadebf43cc23a376a7886e94886cb22..7590eb64049d7875826799ca9b12443e7957963a 100644
--- a/extensions/browser/app_window/app_window.cc
+++ b/extensions/browser/app_window/app_window.cc
@@ -953,6 +953,12 @@ bool AppWindow::IsFullscreenForTabOrPending(const content::WebContents* source)
   return IsHtmlApiFullscreen();
 }
 
+blink::WebDisplayMode AppWindow::GetDisplayMode(
+    const content::WebContents* source) const {
+  return IsFullscreen() ? blink::WebDisplayModeFullscreen :
+                          blink::WebDisplayModeStandalone;
+}
+
 void AppWindow::OnExtensionUnloaded(BrowserContext* browser_context,
                                     const Extension* extension,
                                     UnloadedExtensionInfo::Reason reason) {