FSA: Add WPTs testing FileSystemObserver creation

Bug: 1019297
Change-Id: Ie735d376b760aa78859b1e8c5a1fed1dee90f959
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5200909
Commit-Queue: Austin Sullivan <[email protected]>
Reviewed-by: Daseul Lee <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1250956}

fs/FileSystemObserver.https.tentative.window.js

@@ -0,0 +1,3 @@
+// META: script=/service-workers/service-worker/resources/test-helpers.sub.js
+// META: script=resources/messaging-helpers.js
+// META: script=script-tests/FileSystemObserver.js

fs/resources/message-target.js

@@ -120,6 +120,26 @@ function add_message_event_handlers(receiver, target, target_origin) {
             { targetOrigin: target_origin });
           break;
 
+        case 'create-file-system-observer':
+          // Attempt to create a file system observer with a dummy callback.
+          // Respond with whether creating the observer succeeded.
+          function dummyCallback(records, observer) {};
+
+          let createObserverSuccess = true;
+          try {
+            const observer = new FileSystemObserver(dummyCallback);
+          } catch (error) {
+            createObserverSuccess = false;
+          }
+
+          message_source.postMessage(
+              {
+                type: 'receive-create-file-system-observer-result',
+                createObserverSuccess
+              },
+              {targetOrigin: target_origin});
+          break;
+
         default:
           throw `Unknown message type: '${message_data.type}'`;
       }

fs/script-tests/FileSystemObserver.js

@@ -0,0 +1,57 @@
+'use strict';
+
+// This script depends on the following scripts:
+//    /fs/resources/messaging-helpers.js
+//    /service-worker/resources/test-helpers.sub.js
+
+promise_test(async t => {
+  function dummyCallback(records, observer) {};
+  let success = true;
+  try {
+    const observer = new FileSystemObserver(dummyCallback);
+  } catch (error) {
+    success = false;
+  }
+  assert_true(success);
+}, 'Creating a FileSystemObserver from a window succeeds');
+
+promise_test(async t => {
+  const dedicated_worker =
+      create_dedicated_worker(t, kDedicatedWorkerMessageTarget);
+  dedicated_worker.postMessage({type: 'create-file-system-observer'});
+
+  const event_watcher = new EventWatcher(t, dedicated_worker, 'message');
+  const message_event = await event_watcher.wait_for('message');
+  const response = message_event.data;
+
+  assert_true(response.createObserverSuccess);
+}, 'Creating a FileSystemObserver from a dedicated worker succeeds');
+
+if (self.SharedWorker !== undefined) {
+  promise_test(async t => {
+    const shared_worker = new SharedWorker(kSharedWorkerMessageTarget);
+    shared_worker.port.start();
+    shared_worker.port.postMessage({type: 'create-file-system-observer'});
+
+    const event_watcher = new EventWatcher(t, shared_worker.port, 'message');
+    const message_event = await event_watcher.wait_for('message');
+    const response = message_event.data;
+
+    assert_true(response.createObserverSuccess);
+  }, 'Creating a FileSystemObserver from a shared worker succeeds');
+}
+
+promise_test(async t => {
+  const scope = `${kServiceWorkerMessageTarget}?create-observer`;
+  const registration =
+      await create_service_worker(t, kServiceWorkerMessageTarget, scope);
+  await wait_for_state(t, registration.installing, 'activated');
+
+  registration.active.postMessage({type: 'create-file-system-observer'});
+
+  const event_watcher = new EventWatcher(t, navigator.serviceWorker, 'message');
+  const message_event = await event_watcher.wait_for('message');
+  const response = message_event.data;
+
+  assert_false(response.createObserverSuccess);
+}, 'Creating a FileSystemObserver from a service worker fails');