[Fetch API] Fix leaky layout tests.

third_party/WebKit/LayoutTests/http/tests/fetch/script-tests/response.js

 if (self.importScripts) {
   importScripts('../resources/fetch-test-helpers.js');
   importScripts('/streams/resources/rs-utils.js');
 }
 
 function decode(chunks) {
   var decoder = new TextDecoder();
   var result = '';
   for (var chunk of chunks) {
     result += decoder.decode(chunk, {stream: true});
@@ skipping 300 matching lines @@
 
 test(() => {
     var res = new Response('hello');
     res.body.cancel();
     assert_true(res.bodyUsed);
     assert_throws({name: 'TypeError'}, () => res.clone());
   }, 'Used => clone');
 
 test(() => {
     var res = new Response('hello');
-    res.body.getReader();
+    const reader = res.body.getReader();
     assert_false(res.bodyUsed);
     assert_throws({name: 'TypeError'}, () => res.clone());
+    reader.releaseLock();
   }, 'Locked => clone');
 
 // Tests for MIME types.
 promise_test(function(t) {
     var res = new Response(new Blob(['']));
     return res.blob()
       .then(function(blob) {
           assert_equals(blob.type, '');
           assert_equals(res.headers.get('Content-Type'), null);
         });
@@ skipping 114 matching lines @@
 test(function() {
     ['http://ex\x0aample.com',
      'http://ex\x0dample.com'].forEach(function(url) {
         assert_equals(Response.redirect(url).headers.get('Location'),
                       'http://example.com/',
                       'Location header value must not contain CR or LF');
       });
   }, 'Response.redirect() with URLs with CR or LF');
 
 done();