Record SWR candidates for non SWR revalidation requests.

Revalidation requests would get tagged as SWR candidates when
the revalidation occurred causing skew in the histograms.

BUG=348877

Change-Id: I5d713b9d18513337d7ef9379effda8495ddcad4a
Reviewed-on: https://chromium-review.googlesource.com/c/1334662Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608056}

third_party/blink/renderer/platform/loader/fetch/resource_fetcher.cc

@@ -742,8 +742,9 @@ base::Optional<ResourceRequestBlockedReason> ResourceFetcher::PrepareRequest(
   // stale while revalidate (based on a list of hosts). This allows us
   // to only log metrics for sites that would possibly benefit from
   // stale while revalidate being enabled.
-  resource_request.SetStaleRevalidateCandidate(host_matches_allow ||
-                                               host_matches_control);
+  resource_request.SetStaleRevalidateCandidate(
+      (host_matches_allow || host_matches_control) &&
+      !params.IsStaleRevalidation());
   // Indicate whether the network stack can return a stale resource. If a
   // stale resource is returned a StaleRevalidation request will be scheduled.
   // Explicitly disallow stale responses for fetchers that don't have SWR