Bug 1480903 [wpt PR 12303] - Fix a t.assert_unreached typo in a CSP t…

…est helper, a=testonly

Automatic update from web-platform-testsFix a t.assert_unreached typo in a CSP test helper (#12303)

Found via web-platform-tests/wpt#10877 (comment).
--

wpt-commits: 64a9cbb9aec8db0f84c076ae77045297fe8ea320
wpt-pr: 12303

testing/web-platform/meta/MANIFEST.json

@@ -449293,7 +449293,7 @@
    "support"
   ],
   "content-security-policy/embedded-enforcement/support/testharness-helper.sub.js": [
-   "6d2e64f8f7e9026719e84c8fd1c09dd27c8d03b5",
+   "c1b2e673eced75db5bb3b47abcfef56bff62e465",
    "support"
   ],
   "content-security-policy/font-src/font-match-allowed.sub.html": [

testing/web-platform/tests/content-security-policy/embedded-enforcement/support/testharness-helper.sub.js

@@ -119,11 +119,11 @@ function assert_iframe_with_csp(t, url, csp, shouldBlock, urlId, blockedURI) {
 
   if (shouldBlock) {
     // Assert iframe does not load and is inaccessible.
-    window.onmessage = function (e) {
+    window.onmessage = t.step_func(function(e) {
       if (e.source != i.contentWindow)
           return;
-      t.assert_unreached('No message should be sent from the frame.');
-    }
+      assert_unreached('No message should be sent from the frame.');
+    });
     i.onload = t.step_func(function () {
       // Delay the check until after the postMessage has a chance to execute.
       setTimeout(t.step_func_done(function () {