Introduce WebTransport.Close and WebTransportClient.OnClosed

Introduce network.mojom.WebTransport.Close and
network.mojom.WebTransportClient.OnClosed. They are corresponding to
https://w3c.github.io/webtransport/#session-terminate and
https://w3c.github.io/webtransport/#session-terminated.

We have WPTs that tests this change in
/wpt/webtransport/close.https.any.js. This is skipped as the test server
infrastructure is not ready. Also, the underlying implementation in net/
is not ready so the tests fail even in my local environment.

Bug: 1011392, 1242902, 1242906
Change-Id: I460f1a18815dbeee3720a637d9f496a24aed36d4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3197410
Commit-Queue: Yutaka Hirano <[email protected]>
Reviewed-by: Daniel Cheng <[email protected]>
Reviewed-by: Adam Rice <[email protected]>
Cr-Commit-Position: refs/heads/main@{#927651}

webtransport/close.https.any.js

@@ -32,11 +32,11 @@ promise_test(async t => {
   add_completion_callback(() => wt.close());
   await wt.ready;
 
-  wt.close({code: 99, reason: 'reason'});
+  wt.close({closeCode: 99, reason: 'reason X'});
 
   const close_info = await wt.closed;
 
-  assert_equals(close_info.code, 99, 'code');
+  assert_equals(close_info.closeCode, 99, 'code');
   assert_equals(close_info.reason, 'reason X', 'reason');
 
   await wait(10);
@@ -57,11 +57,11 @@ promise_test(async t => {
   await wt.ready;
   const reason = 'あいうえお'.repeat(1000);
 
-  wt.close({code: 11, reason});
+  wt.close({closeCode: 11, reason});
 
   const close_info = await wt.closed;
 
-  assert_equals(close_info.code, 11, 'code');
+  assert_equals(close_info.closeCode, 11, 'code');
   assert_equals(close_info.reason, reason, 'reason');
 
   await wait(10);