IndexedDB: Move Mojo file to Blink (part 2)

Part 2 in moving the IDB Mojo file from content/common/indexed_db/
to third_party/blink/public/mojom/indexeddb/indexeddb.mojom.

This commit:
- moves IndexedDBKeyPath from content to blink

This commit converts Chromium to the following Mojom types:
- indexed_db.mojom.KeyPath -> blink.mojom.IDBKeyPath

Bug: 717812
Change-Id: I286081555c62c18c5f423813a41035ce8316d494
Reviewed-on: https://chromium-review.googlesource.com/1185790
Commit-Queue: Chase Phillips <cmp@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585946}
40 files changed