Support painting panels with chromium themes on GTK.

chrome/browser/ui/panels/panel_window_controller_cocoa.mm

Index: chrome/browser/ui/panels/panel_window_controller_cocoa.mm
diff --git a/chrome/browser/ui/panels/panel_window_controller_cocoa.mm b/chrome/browser/ui/panels/panel_window_controller_cocoa.mm
index 8a7d4480ba3fe9357ca00c2ad5e36a2fdeaad0be..0d82d62401eeef257264c72378ae37846eefc889 100644
--- a/chrome/browser/ui/panels/panel_window_controller_cocoa.mm
+++ b/chrome/browser/ui/panels/panel_window_controller_cocoa.mm
@@ -886,10 +886,6 @@ enum {
   return NSHeight([titlebar convertRect:[titlebar bounds] toView:nil]);
 }
 
-- (int)titlebarIconOnlyWidthInScreenCoordinates {
-  return [[self titlebarView] iconOnlyWidthInScreenCoordinates];
-}
-
 - (void)ensureFullyVisible {
   // Shows the window without making it key, on top of its layer, even if
   // Chromium is not an active app.