Add methods needed for overflow panels to NativePanel interface.

chrome/browser/ui/panels/panel_browser_view.cc

Index: chrome/browser/ui/panels/panel_browser_view.cc
diff --git a/chrome/browser/ui/panels/panel_browser_view.cc b/chrome/browser/ui/panels/panel_browser_view.cc
index 0a887e2e5106c468c3f6da82f4a9c8dd84b48ee0..cea18f834ac1f2b6a0a2399d6222388bf4ecc6f9 100644
--- a/chrome/browser/ui/panels/panel_browser_view.cc
+++ b/chrome/browser/ui/panels/panel_browser_view.cc
@@ -377,6 +377,15 @@ void PanelBrowserView::DestroyPanelBrowser() {
   DestroyBrowser();
 }
 
+gfx::Size PanelBrowserView::IconOnlySize() const {
+  // TODO(jianli): to be implemented.
+  return gfx::Size();
+}
+
+void PanelBrowserView::EnsurePanelFullyVisible() {
+  // TODO(jianli): to be implemented.
+}
+
 PanelBrowserFrameView* PanelBrowserView::GetFrameView() const {
   return static_cast<PanelBrowserFrameView*>(frame()->GetFrameView());
 }