Clean up unnecessary Create() factory functions in modules/indexeddb

As advised in [1], this CL removes unnecessary Foo::Create() in
//third_party/blink/renderer/modules/indexeddb and make their constructors
public, then make the callers use std::make_unique<Foo> instead
of their Create() factory functions.

[1] https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/iJ1bawbxbWs/vEdfT5QtBgAJ

Bug: 939691
Change-Id: I189e6024d9db77a45793dbaffbf0e77632be2b6f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1525251
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Gyuyoung Kim <gyuyoung@igalia.com>
Cr-Commit-Position: refs/heads/master@{#641178}
21 files changed