Log warning directly.

IPython/html/services/security/handlers.py

@@ -15,7 +15,8 b' class CSPReportHandler(IPythonHandler):'
     def post(self):
         '''Log a content security policy violation report'''
         csp_report = self.get_json_body()
-        self.log.warn(csp_report)
+        self.log.warn("Content security violation: %s",
+                      self.request.body.decode('utf8', 'replace'))
 
 default_handlers = [
     (csp_report_uri, CSPReportHandler)