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

chrome/browser/page_load_metrics/page_load_metrics_observer.h

 // 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.
 
 #ifndef CHROME_BROWSER_PAGE_LOAD_METRICS_PAGE_LOAD_METRICS_OBSERVER_H_
 #define CHROME_BROWSER_PAGE_LOAD_METRICS_PAGE_LOAD_METRICS_OBSERVER_H_
 
 #include <string>
 
 #include "base/macros.h"
@@ skipping 177 matching lines @@
   const base::Optional<base::TimeDelta> page_end_time;
 
   // Extra information supplied to the page load metrics system from the
   // renderer for the main frame.
   const PageLoadMetadata main_frame_metadata;
 
   // PageLoadMetadata for child frames of the current page load.
   const PageLoadMetadata child_frame_metadata;
 };
 
-// Container for various information about a request within a page load.
-struct ExtraRequestInfo {
-  ExtraRequestInfo(bool was_cached,
-                   int64_t raw_body_bytes,
-                   bool data_reduction_proxy_used,
-                   int64_t original_network_content_length);
+// Container for various information about a completed request within a page
+// load.
+struct ExtraRequestCompleteInfo {
+  ExtraRequestCompleteInfo(bool was_cached,
+                           int64_t raw_body_bytes,
+                           bool data_reduction_proxy_used,
+                           int64_t original_network_content_length,
+                           content::ResourceType detected_resource_type);
 
-  ExtraRequestInfo(const ExtraRequestInfo& other);
+  ExtraRequestCompleteInfo(const ExtraRequestCompleteInfo& other);
 
-  ~ExtraRequestInfo();
+  ~ExtraRequestCompleteInfo();
 
   // True if the resource was loaded from cache.
   const bool was_cached;
 
   // The number of body (not header) prefilter bytes.
   const int64_t raw_body_bytes;
 
   // Whether this request used Data Reduction Proxy.
   const bool data_reduction_proxy_used;
 
   // The number of body (not header) bytes that the data reduction proxy saw
   // before it compressed the requests.
   const int64_t original_network_content_length;
+
+  // The type of the request as gleaned from the ResourceRequestInfo.

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

i think someone noted in a previous comment that the resource_type in the
complete info may be more accurate than the value in the start info. If that's
the case, can we note that, and explain in what ways it might be more accurate?
Let's also add a corresponding comment in the resource_type in the start info
that the type in the complete info may be more accurate, so consumers can better
decide which one is more useful for them.

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

Done.

+  const content::ResourceType resource_type;
+};
+
+// Container for various information about a started request within a page load.
+struct ExtraRequestStartInfo {
+  explicit ExtraRequestStartInfo(content::ResourceType type);
+
+  ExtraRequestStartInfo(const ExtraRequestStartInfo& other);
+
+  ~ExtraRequestStartInfo();
+
+  // The type of the request as gleaned from the ResourceRequestInfo.
+  const content::ResourceType resource_type;
 };
 
 // Interface for PageLoadMetrics observers. All instances of this class are
 // owned by the PageLoadTracker tracking a page load.
 class PageLoadMetricsObserver {
  public:
   // ObservePolicy is used as a return value on some PageLoadMetricsObserver
   // callbacks to indicate whether the observer would like to continue observing
   // metric callbacks. Observers that wish to continue observing metric
   // callbacks should return CONTINUE_OBSERVING; observers that wish to stop
@@ skipping 137 matching lines @@
   // frequently on Android).
   virtual void OnComplete(const PageLoadTiming& timing,
                           const PageLoadExtraInfo& extra_info) {}
 
   // OnFailedProvisionalLoad is invoked for tracked page loads that did not
   // commit, immediately before the observer is deleted.
   virtual void OnFailedProvisionalLoad(
       const FailedProvisionalLoadInfo& failed_provisional_load_info,
       const PageLoadExtraInfo& extra_info) {}
 
+  // Called whenever a request load begins.
+  virtual void OnStartedResource(
+      const ExtraRequestStartInfo& extra_request_start_info) {}
+
   // Called whenever a request is loaded for this page load.
-  virtual void OnLoadedResource(const ExtraRequestInfo& extra_request_info) {}
+  virtual void OnLoadedResource(
+      const ExtraRequestCompleteInfo& extra_request_complete_info) {}
 };
 
 }  // namespace page_load_metrics
 
 #endif  // CHROME_BROWSER_PAGE_LOAD_METRICS_PAGE_LOAD_METRICS_OBSERVER_H_