FSA: Fail to create a writable if the file does not exist

DO NOT MERGE (yet) whatwg/fs#125

Currently, the createWritable() algorithm specifies that we must throw
a NotFoundError if the file corresponding to the FileSystemHandle does
not exist. See
https://fs.spec.whatwg.org/#dom-filesystemfilehandle-createwritable

Unfortunately, this does not match the behavior that has been
implemented in Chrome for a very long time; specifically that
- createWritable({ keepExistingData: true }) fails if the file does
  not exist, since there is no existing data to copy to the swap file
- createWritable({ keepExistingData: false }) succeeds if the file
  does not exist, since there is no existing data to copy. It still
  fails if the parent directory does not exist, however

Bug: 1405851
Change-Id: I788c5b177c188862d4b08b5dd876404522fa32d5

fs/script-tests/FileSystemDirectoryHandle-removeEntry.js

@@ -121,15 +121,3 @@ directory_test(async (t, root) => {
   await dir.removeEntry('file-to-remove');
   assert_array_equals(await getSortedDirectoryEntries(dir), ['file-to-keep']);
 }, 'removeEntry() of a directory while a containing file has an open writable fails');
-
-directory_test(async (t, root) => {
-  const handle =
-      await createFileWithContents(t, 'file-to-remove', '12345', root);
-  await root.removeEntry('file-to-remove');
-
-  await promise_rejects_dom(t, 'NotFoundError', cleanup_writable(t, handle.createWritable({keepExistingData: true})));
-
-  assert_array_equals(
-      await getSortedDirectoryEntries(root),
-      []);
-}, 'createWritable after removeEntry succeeds but doesnt recreate the file');

fs/script-tests/FileSystemWritableFileStream.js

@@ -33,6 +33,19 @@ directory_test(async (t, root) => {
   await promise_rejects_dom(t, 'NotFoundError', handle.createWritable());
 }, 'createWritable() fails when parent directory is removed');
 
+directory_test(async (t, root) => {
+  const handle =
+      await createFileWithContents(t, 'file_to_remove.txt', '12345', root);
+  await root.removeEntry('file_to_remove.txt');
+
+  await promise_rejects_dom(
+      t, 'NotFoundError', handle.createWritable({keepExistingData: true}));
+  await promise_rejects_dom(
+      t, 'NotFoundError', handle.createWritable({keepExistingData: false}));
+
+  assert_array_equals(await getSortedDirectoryEntries(root), []);
+}, 'createWritable() fails if the file does not exist');
+
 directory_test(async (t, root) => {
   const handle = await createFileWithContents(
       t, 'atomic_file_is_copied.txt', 'fooks', root);