function TMyRenderProcessHandler.OnBeforeNavigation(
  const browser: ICefBrowser; const frame: ICefFrame;
  const request: ICefRequest; navigationType: TCefNavigationType;
  isRedirect: Boolean): Boolean;
var
  CefMessage: ICefProcessMessage;
begin
  Result := False;

  if (navigationType = NAVIGATION_LINK_CLICKED) then
  begin
    Result := True;
    CefMessage := TCefProcessMessageRef.New('TestMessage');
    browser.SendProcessMessage(PID_BROWSER, CefMessage);
  end;
end;

procedure TForm1.ProcessMessageReceived(Sender: TObject; const browser: ICefBrowser;
  sourceProcess: TCefProcessId; const message: ICefProcessMessage;
  out Result: Boolean);
begin
  if (sourceProcess = PID_RENDERER) and (Message.Name = 'TestMessage') then
    ShowMessage('Message from renderer received...');
end;