IndexedDB: Move kNoTransaction enum to WebIDBCallbacksImpl

Bug: 717812
Change-Id: I4e89bd680673adfe883b49ef218883c4c8a65d87
Reviewed-on: https://chromium-review.googlesource.com/c/1395617
Commit-Queue: Chase Phillips <cmp@chromium.org>
Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621883}
3 files changed