[webnfc] NDEFScanOptions#mediaType being undefined means do not filter (

#21017)

And the empty string should just match on empty.

The spec change:
w3c/web-nfc#496
w3c/web-nfc#498

BUG=520391

Change-Id: Idae55b976a6fbbdd252f6227cbe13ee50d16269c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1986632
Reviewed-by: Rijubrata Bhaumik <rijubrata.bhaumik@intel.com>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Leon Han <leon.han@intel.com>
Cr-Commit-Position: refs/heads/master@{#728813}

Co-authored-by: Han Leon <leon.han@intel.com>

resources/chromium/nfc-mock.js

@@ -133,7 +133,7 @@ function matchesWatchOptions(message, options) {
         options.recordType !== record.recordType) {
       continue;
     }
-    if (options.mediaType !== '' && options.mediaType !== record.mediaType) {
+    if (options.mediaType != null && options.mediaType !== record.mediaType) {
       continue;
     }