Add UMA to track time between preload discovery and reference

third_party/WebKit/Source/core/fetch/FetchRequest.h

Index: third_party/WebKit/Source/core/fetch/FetchRequest.h
diff --git a/third_party/WebKit/Source/core/fetch/FetchRequest.h b/third_party/WebKit/Source/core/fetch/FetchRequest.h
index 1518bbd593a38d4dd9b6d4db3f8d170cc3020a57..a7bbf5a1f9d114eb0b3cd424433e31285cda84fd 100644
--- a/third_party/WebKit/Source/core/fetch/FetchRequest.h
+++ b/third_party/WebKit/Source/core/fetch/FetchRequest.h
@@ -85,7 +85,9 @@ public:
     ClientHintsPreferences& clientHintsPreferences() { return m_clientHintPreferences; }
 
     bool forPreload() const { return m_forPreload; }
-    void setForPreload(bool forPreload) { m_forPreload = forPreload; }
+    void setForPreload(bool forPreload, double discoveryTime = 0);
+
+    double preloadDiscoveryTime() { return m_preloadDiscoveryTime; }
 
     bool isLinkPreload() { return m_linkPreload; }
     void setLinkPreload(bool isLinkPreload) { m_linkPreload = isLinkPreload; }
@@ -104,6 +106,7 @@ private:
     ResourceLoadPriority m_priority;
     bool m_forPreload;
     bool m_linkPreload;
+    double m_preloadDiscoveryTime;
     DeferOption m_defer;
     OriginRestriction m_originRestriction;
     ResourceWidth m_resourceWidth;