Rebaseline virtual/softwarecompositing/fixed-body-background-positioned-expected.txt

For linux only.

TBR=vollick@chromium.org
BUG=

Review URL: https://codereview.chromium.org/185693005

git-svn-id: svn://svn.chromium.org/blink/trunk@168319 bbb929c8-8fbe-4397-9dbb-9b2b20218538