Remove BlobData::Create() in blink

As advised in [1], this CL removes unnecessary BlobData::Create() in
//third_party/blink/renderer/ and make it's constructors public, then
make the callers use std::make_unique<BlobData> instead of their
Create() factory function. Additionally this CL makes to use auto keyword
when creating a local variable by using std::make_unique<BlobData> because
it's clear the returned type is std::unique_ptr.

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

Bug: 939691
Change-Id: Id5800e816128f640f79e1c422ff0b98a57798e89
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1525786
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Gyuyoung Kim <gyuyoung@igalia.com>
Cr-Commit-Position: refs/heads/master@{#641155}
22 files changed