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 a58984656eec1b8effd05e16e67ee570f0d744ab..309817c3441e530fa56a8d1f78b561c7eda358d6 100644
--- a/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
+++ b/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
@@ -252,6 +252,22 @@ PageLoadTracker* MetricsWebContentsObserver::GetTrackerOrNullForRequest(
   return nullptr;
 }
 
+void MetricsWebContentsObserver::OnRequestStarted(
+    const content::GlobalRequestID& request_id,
+    content::ResourceType resource_type,
+    base::TimeTicks creation_time) {
+  // Note for the main HTML page, the tracker may not exist yet, so

[Bryan McQuade, 2017/04/24 13:56:55]

interesting - the fact that the tracker doesn't exist yet is likely an artifact
of the fact that we create trackers in the WillStartRequest callback. Maybe we
should change to creating on DidStartNavigation... can you add a
"TODO(bmcquade): evaluate whether moving tracker creation to DidStartNavigation
would address this" or something similar?

[Pete Williamson, 2017/04/24 19:53:14]

Done.

+  // OnStartedResource will not be called for the main page.  While the main
+  // page is not being tracked today, if we do decide to track it, we will need
+  // to first make sure that GlobalRequestID is set in an earlier callback.
+  PageLoadTracker* tracker =
+      GetTrackerOrNullForRequest(request_id, resource_type, creation_time);
+  if (tracker) {
+    ExtraRequestStartInfo extra_request_start_info(resource_type);
+    tracker->OnStartedResource(extra_request_start_info);
+  }
+}
+
 void MetricsWebContentsObserver::OnRequestComplete(
     const content::GlobalRequestID& request_id,
     content::ResourceType resource_type,
@@ -263,10 +279,10 @@ void MetricsWebContentsObserver::OnRequestComplete(
   PageLoadTracker* tracker =
       GetTrackerOrNullForRequest(request_id, resource_type, creation_time);
   if (tracker) {
-    ExtraRequestInfo extra_request_info(
+    ExtraRequestCompleteInfo extra_request_complete_info(
         was_cached, raw_body_bytes, used_data_reduction_proxy,
-        was_cached ? 0 : original_content_length);
-    tracker->OnLoadedResource(extra_request_info);
+        was_cached ? 0 : original_content_length, resource_type);
+    tracker->OnLoadedResource(extra_request_complete_info);
   }
 }