Revert of Delay Input.dispatchKeyEvent response until after key event ack.

content/public/browser/render_widget_host.h

Index: content/public/browser/render_widget_host.h
diff --git a/content/public/browser/render_widget_host.h b/content/public/browser/render_widget_host.h
index 7005ece92a949acc04ecd59af1e3d9b7e10e8c97..0cda573dd0dbbf3126444ccbee30054cab779341 100644
--- a/content/public/browser/render_widget_host.h
+++ b/content/public/browser/render_widget_host.h
@@ -243,13 +243,12 @@
   virtual void AddMouseEventCallback(const MouseEventCallback& callback) = 0;
   virtual void RemoveMouseEventCallback(const MouseEventCallback& callback) = 0;
 
-  // Observer for WebInputEvents.
+  // Observer for WebInputEvents (but not input event acks).
   class InputEventObserver {
    public:
     virtual ~InputEventObserver() {}
 
-    virtual void OnInputEvent(const blink::WebInputEvent&) {};
-    virtual void OnInputEventAck(const blink::WebInputEvent&) {};
+    virtual void OnInputEvent(const blink::WebInputEvent&) = 0;
   };
 
   // Add/remove an input event observer.