Add ink drop ripple (but no highlight) to comboboxes in harmony.

ui/views/controls/combobox/combobox.h

Index: ui/views/controls/combobox/combobox.h
diff --git a/ui/views/controls/combobox/combobox.h b/ui/views/controls/combobox/combobox.h
index 3de7dc7d880798675fb7c15c307253bc30b74b43..fcfffb309aebdf1bd1684d905f8a1a6c0d81cdb2 100644
--- a/ui/views/controls/combobox/combobox.h
+++ b/ui/views/controls/combobox/combobox.h
@@ -42,7 +42,9 @@ class PrefixSelector;
 // * STYLE_ACTION: clicking on the text notifies the listener. The menu can be
 // shown only by clicking on the arrow. The selected index is always reverted to
 // 0 after the listener is notified.
-class VIEWS_EXPORT Combobox : public PrefixDelegate, public ButtonListener {
+class VIEWS_EXPORT Combobox : public View,
+                              public PrefixDelegate,
+                              public ButtonListener {
  public:
   // The style of the combobox.
   enum Style {