Add Mojo API for Blink hit testing

content/browser/frame_host/input/legacy_ipc_frame_input_handler.h

Index: content/browser/frame_host/input/legacy_ipc_frame_input_handler.h
diff --git a/content/browser/frame_host/input/legacy_ipc_frame_input_handler.h b/content/browser/frame_host/input/legacy_ipc_frame_input_handler.h
index 6ea79e81cedd5cdbba4eb1f56a6ffc5c9316a944..04da599f39b5eac57a33aa8dc603d265f5943706 100644
--- a/content/browser/frame_host/input/legacy_ipc_frame_input_handler.h
+++ b/content/browser/frame_host/input/legacy_ipc_frame_input_handler.h
@@ -47,6 +47,9 @@ class CONTENT_EXPORT LegacyIPCFrameInputHandler
   void AdjustSelectionByCharacterOffset(int32_t start, int32_t end) override;
   void MoveRangeSelectionExtent(const gfx::Point& extent) override;
 
+  void HitTestFrameAt(const gfx::PointF& point,
+                      HitTestFrameAtCallback callback) override;
+
  private:
   void SendInput(std::unique_ptr<IPC::Message> message);