Fix the Views combobox on GTK by adding a new function.

views/controls/combobox/native_combobox_gtk.h

Index: views/controls/combobox/native_combobox_gtk.h
diff --git a/views/controls/combobox/native_combobox_gtk.h b/views/controls/combobox/native_combobox_gtk.h
index 2405697920c903f344154d9718b59d8ca502fe7e..e1034d03721c4d5be6956d5fe6fd606ba5f1c952 100644
--- a/views/controls/combobox/native_combobox_gtk.h
+++ b/views/controls/combobox/native_combobox_gtk.h
@@ -25,12 +25,13 @@ class NativeComboboxGtk : public NativeControlGtk,
   virtual gfx::Size GetPreferredSize() const;
   virtual View* GetView();
   virtual void SetFocus();
+  virtual gfx::NativeView GetTestingHandle() const;
 
  protected:
   // Overridden from NativeControlGtk:
   virtual void CreateNativeControl();
   virtual void NativeControlCreated(GtkWidget* widget);
-  
+
  private:
   // The combobox we are bound to.
   Combobox* combobox_;