Make platform apps use and require a different container ("shell" instead of "panel")

chrome/browser/ui/gtk/browser_window_gtk.cc

Index: chrome/browser/ui/gtk/browser_window_gtk.cc
diff --git a/chrome/browser/ui/gtk/browser_window_gtk.cc b/chrome/browser/ui/gtk/browser_window_gtk.cc
index e3da6b74cd536caf681c7c1fe64e568dc9a78cf2..36669f0deb005ddd2a2db3ce97ae69a78bcd30c8 100644
--- a/chrome/browser/ui/gtk/browser_window_gtk.cc
+++ b/chrome/browser/ui/gtk/browser_window_gtk.cc
@@ -1910,7 +1910,8 @@ void BrowserWindowGtk::ConnectAccelerators() {
 }
 
 void BrowserWindowGtk::UpdateCustomFrame() {
-  gtk_window_set_decorated(window_, !UseCustomFrame());
+  gtk_window_set_decorated(
+      window_, !UseCustomFrame() && browser_->type() != Browser::TYPE_SHELL);
   titlebar_->UpdateCustomFrame(UseCustomFrame() && !IsFullscreen());
   UpdateWindowShape(bounds_.width(), bounds_.height());
 }