cablev2: accept WebSocket continuation frames.

When WebSocket connections pass through our frontend infrastructure their
frames can be fragmented, causing clients to see continuation frames.
Just accept these as data frames; we already handle the |final| flag so
defragmentation already works.

BUG=1002262

Change-Id: I17bea4ddc0a3cd07c558b3d1ca686b449bb9a3b6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2463809
Commit-Queue: Adam Langley <agl@chromium.org>
Reviewed-by: Martin Kreichgauer <martinkr@google.com>
Cr-Commit-Position: refs/heads/master@{#816746}

device/fido/cable/websocket_adapter.cc

@@ -120,7 +120,8 @@ void WebSocketAdapter::OnDataFrame(bool finish,
 
   const size_t old_size = pending_message_.size();
   const size_t new_size = old_size + data_len;
-  if (type != network::mojom::WebSocketMessageType::BINARY ||
+  if ((type != network::mojom::WebSocketMessageType::BINARY &&
+       type != network::mojom::WebSocketMessageType::CONTINUATION) ||
       data_len > std::numeric_limits<uint32_t>::max() || new_size < old_size ||
       new_size > kMaxIncomingMessageSize) {
     FIDO_LOG(ERROR) << "invalid WebSocket frame (type: "