[webnfc] NDEFReadingEvent constructor does not set NDEFRecord#lang

Because NDEFRecord#lang is supposed to be set to the document element's
lang attribute in the original web page that constructs/writes this
record, not in the current web page trying to construct an
NDEFReadingEvent instance.

This CL adds a wpt to guarantee that.

BUG=520391

Change-Id: If609455d6411ee886b74ab7557292c37da41eed6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1930451
Reviewed-by: François Beaufort <beaufort.francois@gmail.com>
Commit-Queue: Leon Han <leon.han@intel.com>
Cr-Commit-Position: refs/heads/master@{#719855}

web-nfc/NDEFReadingEvent_constructor.https.html

@@ -37,4 +37,24 @@
     assertWebNDEFMessagesEqual(event.message, new NDEFMessage(message));
   }, 'NDEFReadingEvent constructor with valid parameters');
 
+  test(() => {
+    const record_init = createTextRecord(test_text_data);
+    const event = new NDEFReadingEvent('type',
+        {serialNumber: '', message: createMessage([record_init])});
+    assert_equals(event.type, 'type', 'type');
+    assert_equals(event.serialNumber, '', 'serialNumber');
+    assert_equals(1, event.message.records.length, 'only 1 record');
+
+    const record = new NDEFRecord(record_init);
+    assert_equals(record.recordType, 'text', 'recordType');
+    assert_equals(record.mediaType, null, 'mediaType');
+    assert_equals(record.encoding, 'utf-8', 'encoding');
+    assert_equals(record.lang, 'en', 'lang');
+
+    assert_equals(event.message.records[0].recordType, 'text', 'recordType');
+    assert_equals(event.message.records[0].mediaType, null, 'mediaType');
+    assert_equals(event.message.records[0].encoding, 'utf-8', 'encoding');
+    assert_equals(event.message.records[0].lang, null, 'lang is not set');
+  }, 'NDEFReadingEvent constructor does not set NDEFRecord#lang for any text records it embeds');
+
 </script>