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 0689b136685651ce0300c4aef4bb2438961ce7ac..4fcde59d23dcd12d434f733593d6f961a3372eb9 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) {