Set was_fetched_via_cache when we set was_in_prefetch_cache

Currently when a main SXG is served from PrefetchedSignedExchangeCache
was_in_prefetch_cache flag is set, but was_fetched_via_cache flag is not
set. So "Cached" suffixed PageLoad.Clients.SignedExchange UMAs are not
recorded.

To fix this, this CL set was_fetched_via_cache flag when we set
was_in_prefetch_cache flag.

Bug: 935267
Change-Id: I22bbd9554b871ad1f1c9e3268af113ed9c22de59
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1696961Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Tsuyoshi Horo <horo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#676299}

content/browser/web_package/prefetched_signed_exchange_cache.cc

@@ -85,6 +85,7 @@ class RedirectResponseURLLoader : public network::mojom::URLLoader {
     network::ResourceResponseHead response_head =
         signed_exchange_utils::CreateRedirectResponseHead(
             outer_response, false /* is_fallback_redirect */);
+    response_head.was_fetched_via_cache = true;
     response_head.was_in_prefetch_cache = true;
     UpdateRequestResponseStartTime(&response_head);
     client_->OnReceiveRedirect(signed_exchange_utils::CreateRedirectInfo(

content/browser/web_package/prefetched_signed_exchange_cache_adapter.cc

@@ -52,6 +52,7 @@ void PrefetchedSignedExchangeCacheAdapter::OnReceiveInnerResponse(
     const network::ResourceResponseHead& response) {
   std::unique_ptr<network::ResourceResponseHead> inner_response =
       std::make_unique<network::ResourceResponseHead>(response);
+  inner_response->was_fetched_via_cache = true;
   inner_response->was_in_prefetch_cache = true;
   cached_exchange_->SetInnerResponse(std::move(inner_response));
 }