Fix crash in WebSocketChannel::ReadFrames

RespondToClosingHandshake can fail, and in that case we must stop using
the net::WebSocketChannel instance.

Bug: 994000
Change-Id: Ibaba2c552cfba59c3d95f63f0d9e807df4c4f564
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1830492
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Adam Rice <ricea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#701047}

net/websockets/websocket_channel.cc

@@ -594,7 +594,9 @@ ChannelState WebSocketChannel::ReadFrames() {
     DCHECK(!event_interface_->HasPendingDataFrames());
     // We've been waiting for the client to consume the frames before
     // responding to the closing handshake initiated by the server.
-    ignore_result(RespondToClosingHandshake());
+    if (RespondToClosingHandshake() == CHANNEL_DELETED) {
+      return CHANNEL_DELETED;
+    }
   }
 
   // TODO(crbug.com/999235): Remove this CHECK.