Create PrefetchServingPageMetricsContainer in NavigationRequest

This CL

- Removes dependencies from `PrefetchServingPageMetrics`
  to `PrefetchDocumentManager::DidStartNavigation()`.
- Creates and records the metrics for
  prefetch-in-new-tab cases (crbug.com/1432886).

Before this CL, `PrefetchServingPageMetricsContainer`
is created and set to `PrefetchContainer` in
`PrefetchDocumentManager::DidStartNavigation()`.

After this CL, `PrefetchServingPageMetricsContainer`
is created in `NavigationRequest`,
plumbed to `NavigationRequestInfo`
-> `PrefetchURLLoaderInterceptor`
-> `PrefetchService::GetPrefetchToServe()`,
and set to `PrefetchContainer` there.

This CL creates `PrefetchServingPageMetricsContainer`
even if `PrefetchDocumentManager::DidStartNavigation()`
isn't called, but still creates the metrics container
only when the initiator Document has its
`PrefetchDocumentManager`,
in order to avoid recording the metrics
for much broader range of Documents where
speculation rules prefetch is not used at all.

`SetMetricsForPossibleNoVarySearchHintMatches()`
is no longer needed, as all potential matches
including No-Vary-Search hint candidates are iterated
in `PrefetchService::FindPrefetchContainerToServe()`.

Bug: 1494728, 1432886, 1448731
Change-Id: I7227b342c8750ede64cdcdeb6c32ea0c0601db85
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4953788
Reviewed-by: Max Curran <curranmax@chromium.org>
Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Reviewed-by: Lingqi Chi <lingqi@chromium.org>
Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Commit-Queue: Hiroshige Hayashizaki <hiroshige@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1217797}