Move FetchContext::RecordLoadingActivity to ResourceLoadObserver

Rename it to ResourceLoadObserver::DidStartRequest.

Bug: 914739
Change-Id: I0313c2fed3f474121a962007a568a078fbb5335b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1538065
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#667848}
12 files changed