Add ServiceWorker error enums
Add ServiceWorker error enums

Flushing out actual error conditions that can be thrown by the backend.

BUG=
TBR=abarth@chromium.org

Review URL: https://codereview.chromium.org/107293009

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@163811 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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