Add UMA to track time between preload discovery and reference

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

Index: third_party/WebKit/Source/core/fetch/Resource.h
diff --git a/third_party/WebKit/Source/core/fetch/Resource.h b/third_party/WebKit/Source/core/fetch/Resource.h
index 0470e67213294d9dfea5f630861b89ad9d7fd8cc..9901587d42aaafbcd9b737720bea0dc751a679b2 100644
--- a/third_party/WebKit/Source/core/fetch/Resource.h
+++ b/third_party/WebKit/Source/core/fetch/Resource.h
@@ -105,6 +105,8 @@ public:
     void setLinkPreload(bool isLinkPreload) { m_linkPreload = isLinkPreload; }
     bool isLinkPreload() const { return m_linkPreload; }
 
+    void setPreloadDiscoveryTime(double preloadDiscoveryTime) { m_preloadDiscoveryTime = preloadDiscoveryTime; }
+
     const ResourceError& resourceError() const { return m_error; }
 
     void setIdentifier(unsigned long identifier) { m_identifier = identifier; }
@@ -333,6 +335,8 @@ private:
 
     unsigned m_preloadCount;
 
+    double m_preloadDiscoveryTime;
+
     String m_cacheIdentifier;
 
     unsigned m_preloadResult : 2; // PreloadResult