IndexedDB: Avoid side effects for array key conversion w/ HasOwnProperty

      When converting arrays to keys, only own properties should be
considered, much like clones. Otherwise, this opens up the behavior to
side effects via getters on the Object/Array prototype even if the
value being converted to a key is a clone.

BUG=641101
R=haraken@chromium.org

Review-Url: https://codereview.chromium.org/2279343002
Cr-Commit-Position: refs/heads/master@{#415172}