[PageLoadMetrics] Record bytes usage per page

chrome/browser/page_load_metrics/page_load_metrics_observer.h

Index: chrome/browser/page_load_metrics/page_load_metrics_observer.h
diff --git a/chrome/browser/page_load_metrics/page_load_metrics_observer.h b/chrome/browser/page_load_metrics/page_load_metrics_observer.h
index 7d4c1af22284e8a4bf76a4eceb04160ef110cacc..3e7bbf5a2ca23267083d7d7c933bf09c4cd7bb42 100644
--- a/chrome/browser/page_load_metrics/page_load_metrics_observer.h
+++ b/chrome/browser/page_load_metrics/page_load_metrics_observer.h
@@ -118,6 +118,8 @@ struct PageLoadExtraInfo {
       const base::Optional<base::TimeDelta>& time_to_abort,
       int num_cache_requests,
       int num_network_requests,
+      int64_t cache_bytes,
+      int64_t net_bytes,
       const PageLoadMetadata& metadata);
 
   PageLoadExtraInfo(const PageLoadExtraInfo& other);
@@ -168,6 +170,11 @@ struct PageLoadExtraInfo {
   int num_cache_requests;
   int num_network_requests;
 
+  // The number of body (not header) prefilter bytes consumed by requests for
+  // the page.
+  int64_t cache_bytes;
+  int64_t network_bytes;
+
   // Extra information supplied to the page load metrics system from the
   // renderer.
   const PageLoadMetadata metadata;
@@ -298,7 +305,8 @@ class PageLoadMetricsObserver {
   // OnComplete is invoked for tracked page loads that committed, immediately
   // before the observer is deleted. Observers that implement OnComplete may
   // also want to implement FlushMetricsOnAppEnterBackground, to avoid loss of
-  // data if the application is killed while in the background.
+  // data if the application is killed while in the background (this happens
+  // frequently on Android).
   virtual void OnComplete(const PageLoadTiming& timing,
                           const PageLoadExtraInfo& extra_info) {}