Add reporting.idl as a dep for CSP idlharness.js tests (#15864)

Needed for https://github.com/web-platform-tests/wpt/pull/15856.
diff --git a/content-security-policy/securitypolicyviolation/idlharness.window.js b/content-security-policy/securitypolicyviolation/idlharness.window.js
index fc5e65d..25efd0d 100644
--- a/content-security-policy/securitypolicyviolation/idlharness.window.js
+++ b/content-security-policy/securitypolicyviolation/idlharness.window.js
@@ -7,7 +7,7 @@
 
 idl_test(
   ['CSP'],
-  ['dom'],
+  ['dom', 'reporting'],
   idl_array => {
     idl_array.add_objects({
       SecurityPolicyViolationEvent: [