Add methods needed for overflow panels to NativePanel interface.

chrome/browser/ui/panels/panel_browser_window_gtk.cc

Index: chrome/browser/ui/panels/panel_browser_window_gtk.cc
diff --git a/chrome/browser/ui/panels/panel_browser_window_gtk.cc b/chrome/browser/ui/panels/panel_browser_window_gtk.cc
index 68db6feace21e62f2c04fa2fd871e9da16f905d8..0726ba3e07274decd5d322b7d234a42dde16b680 100644
--- a/chrome/browser/ui/panels/panel_browser_window_gtk.cc
+++ b/chrome/browser/ui/panels/panel_browser_window_gtk.cc
@@ -371,6 +371,15 @@ void PanelBrowserWindowGtk::DestroyPanelBrowser() {
   DestroyBrowser();
 }
 
+gfx::Size PanelBrowserWindowGtk::IconOnlySize() const {
+  // TODO(prasdt): to be implemented.
+  return gfx::Size();
+}
+
+void PanelBrowserWindowGtk::EnsurePanelFullyVisible() {
+  // TODO(prasdt): to be implemented.
+}
+
 gfx::Size PanelBrowserWindowGtk::WindowSizeFromContentSize(
     const gfx::Size& content_size) const {
   gfx::Size frame = GetNonClientFrameSize();