Send an event to the page load metrics to track resource starting.

chrome/browser/page_load_metrics/metrics_web_contents_observer.cc

Index: chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
diff --git a/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc b/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
index e3f51bf4946a1b2cc9437a0e973f4b77a78e5325..2fb5d27aebda73ace023bbe3dadb5e09145d4292 100644
--- a/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
+++ b/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
@@ -244,6 +244,20 @@ PageLoadTracker* MetricsWebContentsObserver::GetTrackerOrNullForRequest(
   return nullptr;
 }
 
+void MetricsWebContentsObserver::OnRequestStarted(
+    const content::GlobalRequestID& request_id,
+    content::ResourceType resource_type,
+    base::TimeTicks creation_time) {
+  PageLoadTracker* tracker =
+      GetTrackerOrNullForRequest(request_id, resource_type, creation_time);
+  if (tracker) {
+    ExtraRequestInfo extra_request_info(

[RyanSturm, 2017/03/29 19:03:47]

Debatable whether the two request methods should share a struct or each have
their own. Perhaps ExtraRequestStartInfo and ExtraRequestCompleteInfo. I'm not
sure how much this information will overlap because it seems like only
content::Type would be share right now.

[Pete Williamson, 2017/04/13 23:10:21]

OK, I'll separate it into two types (and add the request_type to the both)

+        false /*was_cached*/, 0 /*raw_body_bytes*/,
+        false /*used_data_reduction_proxy*/, 0 /*original_content_length*/);
+    tracker->OnStartedResource(extra_request_info);
+  }
+}
+
 void MetricsWebContentsObserver::OnRequestComplete(
     const content::GlobalRequestID& request_id,
     content::ResourceType resource_type,