Make FetchContext::GetSecurityOrigin() non-virtual

This CL introduces FetchContext::fetch_client_settings_object_ and makes
- FetchContext::GetSecurityOrigin()
- FetchContext::GetFetchClientSettingsObject()
non-virtual, to make it clearer that FetchContext's SecurityOrigin
is always the SecurityOrigin of FetchContext's FetchClientSettingsObject.

Bug: 880027
Change-Id: I7ea1cc0edd4d7096b3a0c009c24fcb140d275430
Reviewed-on: https://chromium-review.googlesource.com/c/1352042
Commit-Queue: Hiroshige Hayashizaki <hiroshige@chromium.org>
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#614282}
10 files changed