IndexedDB: Use WebIDBCallbacks to implement the IDBCallbacks interface

IndexedDBCallbacksImpl was originally an implementation of the Mojo
IDBCallbacks interface hosted by the renderer process defined in
content/renderer/.  In onion souping IndexedDB, all of the Mojo
interfaces moved to be hosted in blink/renderer/modules/indexeddb/,
which made the extra layer of IndexedDBCallbacksImpl redundant with
WebIDBCallbacks.

This commit removes the redundant layer, moving the Mojo IDBCallbacks
interface from IndexedDBCallbacksImpl to WebIDBCallbacks.

Bug: 717812
Change-Id: I076002f019f2cf9e5ddb965c504615c8ed60fcf9
Reviewed-on: https://chromium-review.googlesource.com/c/1395558
Commit-Queue: Chase Phillips <cmp@chromium.org>
Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622116}
17 files changed