s/GURL origin_url/url::Origin origin/ in FileSystemManagerImpl::Open.

This CL makes small improvements in type safety:
- url::Origin should be used instead of GURL for representing an origin.
- url::Origin::Create(gurl) should be used instead of GURL::GetOrigin()
  (the latter will return "physical/syntactical" origin which would be
   incorrect in case of blob: and filesystem: URLs)

Bug: 917457
Change-Id: I97a0fe063461ea340476914502f31581ff676688
Reviewed-on: https://chromium-review.googlesource.com/c/1406171
Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
Reviewed-by: Nasko Oskov <nasko@chromium.org>
Commit-Queue: Ɓukasz Anforowicz <lukasza@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622236}
7 files changed