[SOUP] Fix the build if !ENABLE(WEB_TIMING)
https://bugs.webkit.org/show_bug.cgi?id=127906

Reviewed by Gustavo Noronha Silva.

* platform/network/soup/SoupNetworkSession.cpp:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@163081 268f45cc-cd09-0410-ab3c-d52691b4dbfc