GitLab

SubstitutionPatterm -> SubstitutionPattern
SubstutitionWriter -> SubstitutionWriter

BUG=None
TEST=ninja -C out/Debug gn_unittests - compare the output before and
after this change.
TBR=brettw@chromium.org

Review URL: https://codereview.chromium.org/590683002

Cr-Commit-Position: refs/heads/master@{#295846}