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

chrome/browser/loader/chrome_resource_dispatcher_host_delegate.cc

Index: chrome/browser/loader/chrome_resource_dispatcher_host_delegate.cc
diff --git a/chrome/browser/loader/chrome_resource_dispatcher_host_delegate.cc b/chrome/browser/loader/chrome_resource_dispatcher_host_delegate.cc
index a9d0044df47a9a7af6fe433e9725592283b97c8f..1ba0e3c369da44aead35ba54b34edeb51b460eb1 100644
--- a/chrome/browser/loader/chrome_resource_dispatcher_host_delegate.cc
+++ b/chrome/browser/loader/chrome_resource_dispatcher_host_delegate.cc
@@ -354,6 +354,24 @@ void LogMainFrameMetricsOnUIThread(const GURL& url,
   }
 }
 
+void NotifyUIThreadOfRequestStarted(
+    const content::ResourceRequestInfo::WebContentsGetter& web_contents_getter,
+    const GURL& url,

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

Are you using url here?

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

Done.

+    const content::GlobalRequestID& request_id,
+    ResourceType resource_type,
+    base::TimeTicks request_creation_time) {
+  content::WebContents* web_contents = web_contents_getter.Run();
+
+  page_load_metrics::MetricsWebContentsObserver* metrics_observer =
+      page_load_metrics::MetricsWebContentsObserver::FromWebContents(
+          web_contents);
+
+  if (metrics_observer) {
+    metrics_observer->OnRequestStarted(request_id, resource_type,
+                                       request_creation_time);
+  }
+}
+
 void NotifyUIThreadOfRequestComplete(
     const content::ResourceRequestInfo::WebContentsGetter& web_contents_getter,
     const GURL& url,
@@ -442,6 +460,9 @@ bool ChromeResourceDispatcherHostDelegate::ShouldBeginRequest(
   return true;
 }
 
+// TODO: REVIEWERS: appcache_service is apparently not used.  Is there any
+// reason that I shouldn't remove it? (Maybe it's a part of some interface used
+// elsewhere.)
 void ChromeResourceDispatcherHostDelegate::RequestBeginning(
     net::URLRequest* request,
     content::ResourceContext* resource_context,
@@ -453,6 +474,15 @@ void ChromeResourceDispatcherHostDelegate::RequestBeginning(
 
   const ResourceRequestInfo* info = ResourceRequestInfo::ForRequest(request);
 
+  // TODO(petewil): Unify the safe browsing request and the metrics observer
+  // request if possible so we only have to cross to the main thread once.
+  BrowserThread::PostTask(
+      BrowserThread::UI, FROM_HERE,
+      base::Bind(&NotifyUIThreadOfRequestStarted,
+                 info->GetWebContentsGetterForRequest(), request->url(),
+                 info->GetGlobalRequestID(), info->GetResourceType(),
+                 request->creation_time()));
+
 // The lowering of request priority causes issues with scheduling, since
 // content::ResourceScheduler uses it to delay and throttle requests. This is
 // disabled only on Android, as the prerenders are not likely to compete with