Optimizes the operation of DeleteDatabase when no backing store exists.

When deleting the non existing database in a origin with no existing
backing store, then in DeleteDatabse(), early exiting before OpenBackingStore,
so that it wont results in multiple transaction as earlier.

BUG=460236

Review URL: https://codereview.chromium.org/1071553002

Cr-Commit-Position: refs/heads/master@{#326473}
2 files changed