[NativeFS] Update permissions API following spec change.

This implements the changes from https://github.com/WICG/native-file-system/pull/200.

Change-Id: I9702f9888c4f0fff2084143ac6077b8484dfce16
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2298296
Reviewed-by: Trent Apted <tapted@chromium.org>
Reviewed-by: Will Harris <wfh@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Commit-Queue: Marijn Kruisselbrink <mek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#792004}
diff --git a/native-file-system/resources/messaging-serialize-helpers.js b/native-file-system/resources/messaging-serialize-helpers.js
index 3ef347f..3df2d48 100644
--- a/native-file-system/resources/messaging-serialize-helpers.js
+++ b/native-file-system/resources/messaging-serialize-helpers.js
@@ -31,10 +31,10 @@
 // FileSystemDirectoryHandle.
 async function serialize_file_system_handle(handle) {
   const read_permission =
-    await handle.queryPermission({ writable: false });
+    await handle.queryPermission({ mode: 'read' });
 
   const write_permission =
-    await handle.queryPermission({ writable: true })
+    await handle.queryPermission({ mode: 'readwrite' })
 
   return {
     kind: handle.kind,
diff --git a/native-file-system/resources/native-fs-test-helpers.js b/native-file-system/resources/native-fs-test-helpers.js
index cd1613e..1f944b0 100644
--- a/native-file-system/resources/native-fs-test-helpers.js
+++ b/native-file-system/resources/native-fs-test-helpers.js
@@ -41,14 +41,14 @@
 }
 
 directory_test(async (t, dir) => {
-  assert_equals(await dir.queryPermission({writable: false}), 'granted');
+  assert_equals(await dir.queryPermission({mode: 'read'}), 'granted');
 }, 'User succesfully selected an empty directory.');
 
 directory_test(async (t, dir) => {
-  const status = await dir.queryPermission({writable: true});
+  const status = await dir.queryPermission({mode: 'readwrite'});
   if (status == 'granted')
     return;
 
   await window.test_driver.bless('ask for write permission');
-  assert_equals(await dir.requestPermission({writable: true}), 'granted');
+  assert_equals(await dir.requestPermission({mode: 'readwrite'}), 'granted');
 }, 'User granted write access.');
diff --git a/native-file-system/showSaveFilePicker-manual.https.html b/native-file-system/showSaveFilePicker-manual.https.html
index 022f677..451a0fb 100644
--- a/native-file-system/showSaveFilePicker-manual.https.html
+++ b/native-file-system/showSaveFilePicker-manual.https.html
@@ -26,7 +26,7 @@
 
     promise_test(async t => {
       assert_equals(await file.queryPermission(), 'granted');
-      assert_equals(await file.queryPermission({ writable: true }), 'granted');
+      assert_equals(await file.queryPermission({ mode: 'readwrite' }), 'granted');
     }, 'showSaveFilePicker returns correct permissions');
   }, 'showSaveFilePicker works');