[Attempt 2] Inform Chrome client of changes to an input's datalist.

public/web/WebAutofillClient.h

Index: public/web/WebAutofillClient.h
diff --git a/public/web/WebAutofillClient.h b/public/web/WebAutofillClient.h
index 7fef5f0ad72081e51d3ad38e677ae89c66311d10..b77b386622fc5541155e1549142907790a12a8b0 100644
--- a/public/web/WebAutofillClient.h
+++ b/public/web/WebAutofillClient.h
@@ -52,6 +52,8 @@ public:
     virtual void textFieldDidReceiveKeyDown(const WebInputElement&, const WebKeyboardEvent&) { }
     // This is called when a datalist indicator is clicked.
     virtual void openTextDataListChooser(const WebInputElement&) { }
+    // This is called when the datalist for an input has changed.
+    virtual void dataListOptionsChanged(const WebInputElement&) { }
     // Called the first time the user interacts with the page after a load.
     virtual void firstUserGestureObserved() { }