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

chrome/browser/page_load_metrics/metrics_web_contents_observer.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/page_load_metrics/metrics_web_contents_observer.h"
 
 #include <algorithm>
 #include <ostream>
 #include <string>
 #include <utility>
@@ skipping 234 matching lines @@
     // investigation is needed to confirm that all cases would be handled
     // correctly (for example Link: preloads).
     if (committed_load_ &&
         creation_time >= committed_load_->navigation_start()) {
       return committed_load_.get();
     }
   }
   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,
     bool was_cached,
     bool used_data_reduction_proxy,
     int64_t raw_body_bytes,
     int64_t original_content_length,
     base::TimeTicks creation_time) {
   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);
   }
 }
 
 void MetricsWebContentsObserver::OnNavigationDelayComplete(
     content::NavigationHandle* navigation_handle,
     base::TimeDelta scheduled_delay,
     base::TimeDelta actual_delay) {
   auto it = provisional_loads_.find(navigation_handle);
   if (it == provisional_loads_.end())
     return;
@@ skipping 304 matching lines @@
     content::NavigationHandle* navigation_handle) const {
   DCHECK(navigation_handle->IsInMainFrame());
   DCHECK(!navigation_handle->HasCommitted() ||
          !navigation_handle->IsSameDocument());
 
   return BrowserPageTrackDecider(embedder_interface_.get(), web_contents(),
                                  navigation_handle).ShouldTrack();
 }
 
 }  // namespace page_load_metrics