ui: Cleanup class/struct forward declarations

content/browser/renderer_host/input/mock_input_router_client.h

Index: content/browser/renderer_host/input/mock_input_router_client.h
diff --git a/content/browser/renderer_host/input/mock_input_router_client.h b/content/browser/renderer_host/input/mock_input_router_client.h
index f3cf5529a2b2d8bfa4181d9fe719be0d68b58899..463d7f694f44231c55dde8109cd836f33062760e 100644
--- a/content/browser/renderer_host/input/mock_input_router_client.h
+++ b/content/browser/renderer_host/input/mock_input_router_client.h
@@ -28,7 +28,7 @@ class MockInputRouterClient : public InputRouterClient {
       const ui::LatencyInfo& latency_info) override;
   void IncrementInFlightEventCount(
       blink::WebInputEvent::Type event_type) override;
-  void DecrementInFlightEventCount() override;
+  void DecrementInFlightEventCount(InputEventAckSource ack_source) override;
   void OnHasTouchEventHandlers(bool has_handlers) override;
   void DidFlush() override;
   void DidOverscroll(const ui::DidOverscrollParams& params) override;