Add clean up logic to navigator.credentials layout tests

third_party/WebKit/LayoutTests/http/tests/credentialmanager/credentialscontainer-frame-errors.html

Index: third_party/WebKit/LayoutTests/http/tests/credentialmanager/credentialscontainer-frame-errors.html
diff --git a/third_party/WebKit/LayoutTests/http/tests/credentialmanager/credentialscontainer-frame-errors.html b/third_party/WebKit/LayoutTests/http/tests/credentialmanager/credentialscontainer-frame-errors.html
index a18f50f28e58f5806394513450a8f737d858d58f..4a1a5cc73e804dce7fb70a42a09dce7e8179a91f 100644
--- a/third_party/WebKit/LayoutTests/http/tests/credentialmanager/credentialscontainer-frame-errors.html
+++ b/third_party/WebKit/LayoutTests/http/tests/credentialmanager/credentialscontainer-frame-errors.html
@@ -3,6 +3,11 @@
 <script src="../resources/testharness.js"></script>
 <script src="../resources/testharnessreport.js"></script>
 <script>
+add_completion_callback(() => {
+    if (window.testRunner)
+        window.testRunner.clearMockCredentialManagerResponse();
+});
+
 function create_iframe_test(origin) {
     return function (t) {
         window.addEventListener("load", _ => {
@@ -26,4 +31,3 @@ function create_iframe_test(origin) {
 async_test(create_iframe_test("http://127.0.0.1:8000"), "Same-origin IFrame throws.");
 async_test(create_iframe_test("http://example.test:8000"), "Cross-origin IFrame throws.");
 </script>
-