First version of PerformanceObserver

Source/core/timing/PerformanceUserTiming.h

Index: Source/core/timing/PerformanceUserTiming.h
diff --git a/Source/core/timing/PerformanceUserTiming.h b/Source/core/timing/PerformanceUserTiming.h
index af68d36b5620f423409e86609544aae7f6693ebc..c2da08e0c60f2b69acbb0dd576bd810730225e8d 100644
--- a/Source/core/timing/PerformanceUserTiming.h
+++ b/Source/core/timing/PerformanceUserTiming.h
@@ -38,6 +38,7 @@ class PerformanceBase;
 
 typedef unsigned long long (PerformanceTiming::*NavigationTimingFunction)() const;
 using PerformanceEntryMap = HeapHashMap<String, PerformanceEntryVector>;
+using NewPerformanceEntryCallback = PassOwnPtr<Function<void(PerformanceEntry*)>>;
 
 class UserTiming final : public GarbageCollected<UserTiming> {
 public:
@@ -46,10 +47,10 @@ public:
         return new UserTiming(performance);
     }
 
-    void mark(const String& markName, ExceptionState&);
+    void mark(const String& markName, NewPerformanceEntryCallback, ExceptionState&);
     void clearMarks(const String& markName);
 
-    void measure(const String& measureName, const String& startMark, const String& endMark, ExceptionState&);
+    void measure(const String& measureName, const String& startMark, const String& endMark, NewPerformanceEntryCallback, ExceptionState&);
     void clearMeasures(const String& measureName);
 
     PerformanceEntryVector getMarks() const;