Correctly handle extensions width in the GTK extension shelf.

chrome/browser/gtk/extension_view_gtk.h

Index: chrome/browser/gtk/extension_view_gtk.h
diff --git a/chrome/browser/gtk/extension_view_gtk.h b/chrome/browser/gtk/extension_view_gtk.h
index b569c039bf61c77ecd40580382b7e432619cd432..1220873289265ff1401af1689a58cad8ea6d50f2 100644
--- a/chrome/browser/gtk/extension_view_gtk.h
+++ b/chrome/browser/gtk/extension_view_gtk.h
@@ -21,6 +21,10 @@ class ExtensionViewGtk {
   bool is_toolstrip() const { return is_toolstrip_; }
   void set_is_toolstrip(bool is_toolstrip) { is_toolstrip_ = is_toolstrip; }
 
+  // Method for the ExtensionHost to notify us about the correct width for
+  // extension contents.
+  void UpdatePreferredWidth(int pref_width);
+
  private:
   RenderViewHost* render_view_host() const;