Add Mojo API for Blink hit testing

content/renderer/render_widget.h

Index: content/renderer/render_widget.h
diff --git a/content/renderer/render_widget.h b/content/renderer/render_widget.h
index b7ce5d32bb4a3c6afc9b497e07627207f6ffe98b..da5723dd5ab8002ca495155a4fb2df8ed13e5898 100644
--- a/content/renderer/render_widget.h
+++ b/content/renderer/render_widget.h
@@ -429,6 +429,8 @@ class CONTENT_EXPORT RenderWidget
   // Requests a BeginMainFrame callback from the compositor.
   void SetNeedsMainFrame() override;
 
+  int HitTestFrameAt(const gfx::Point& point);
+
   void HandleInputEvent(const blink::WebCoalescedInputEvent& input_event,
                         const ui::LatencyInfo& latency_info,
                         HandledEventCallback callback) override;