[NoStatePrefetch] Add performance histograms.
This CL adds histograms to record performance of NoStatePrefetch.
The histograms added are:
NoStatePrefetchAge: age of the prefetch when it is used
NoStatePrefetchTTFCP: Time To First Contentful Paint, with variations:
- Cold/Warm/Reference:
* Warm: Prefetch is recent enough to skip revalidation
* Cold: Prefetch is old and does not skip revalidation
* Reference: there was no prefetch
- Cacheable/NoStore: whether the main resource had "no-store" headers.
BUG=642371
TBR=jochen
Review-Url: https://codereview.chromium.org/2321083002
Cr-Commit-Position: refs/heads/master@{#419733}
diff --git a/chrome/browser/BUILD.gn b/chrome/browser/BUILD.gn
index 1ac5c43..196e615 100644
--- a/chrome/browser/BUILD.gn
+++ b/chrome/browser/BUILD.gn
@@ -696,6 +696,8 @@
"page_load_metrics/observers/https_engagement_metrics/https_engagement_service.h",
"page_load_metrics/observers/https_engagement_metrics/https_engagement_service_factory.cc",
"page_load_metrics/observers/https_engagement_metrics/https_engagement_service_factory.h",
+ "page_load_metrics/observers/no_state_prefetch_page_load_metrics_observer.cc",
+ "page_load_metrics/observers/no_state_prefetch_page_load_metrics_observer.h",
"page_load_metrics/observers/previews_page_load_metrics_observer.cc",
"page_load_metrics/observers/previews_page_load_metrics_observer.h",
"page_load_metrics/observers/service_worker_page_load_metrics_observer.cc",
