Make Pepper WebSocket UtilityGetProtocol test less flaky by making the wsh wait for close

Attempt to fix the flakiness by making sure the server handler doesn't exit
before the client closes.

BUG=389084
R=jgraettinger,yhirano

Review URL: https://codereview.chromium.org/410383003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@285500 0039d316-1c4b-4281-b951-d872f2087c98

net/data/websocket/protocol-test_wsh.py

@@ -17,3 +17,5 @@ def web_socket_do_extra_handshake(request):
 
 def web_socket_transfer_data(request):
   msgutil.send_message(request, request.ws_protocol)
+  # Wait for a close message.
+  unused = request.ws_stream.receive_message()