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

ui/views/controls/prefix_selector.h

Index: ui/views/controls/prefix_selector.h
diff --git a/ui/views/controls/prefix_selector.h b/ui/views/controls/prefix_selector.h
index 9476855534cb8e6c915e1448e372ced9e13f2c50..76f61419bdf0698495b9428596c2a984c70d943f 100644
--- a/ui/views/controls/prefix_selector.h
+++ b/ui/views/controls/prefix_selector.h
@@ -17,12 +17,13 @@
 namespace views {
 
 class PrefixDelegate;
+class View;
 
 // PrefixSelector is used to change the selection in a view as the user
 // types characters.
 class VIEWS_EXPORT PrefixSelector : public ui::TextInputClient {
  public:
-  explicit PrefixSelector(PrefixDelegate* delegate);
+  PrefixSelector(PrefixDelegate* delegate, View* host_view);
   ~PrefixSelector() override;
 
   // Invoked from the view when it loses focus.
@@ -71,6 +72,8 @@ class VIEWS_EXPORT PrefixSelector : public ui::TextInputClient {
 
   PrefixDelegate* prefix_delegate_;
 
+  View* host_view_;
+
   // Time OnTextInput() was last invoked.
   base::TimeTicks time_of_last_key_;