LibWeb: Implement PerformanceObserver

Author: https://github.com/Lubrsi
Commit: af2886449a
Pull-request: https://github.com/SerenityOS/serenity/pull/20760
Reviewed-by: https://github.com/kalenikaliaksandr

Userland/Libraries/LibWeb/PerformanceTimeline/PerformanceEntryTuple.h

@@ -14,7 +14,7 @@ namespace Web::PerformanceTimeline {
 struct PerformanceEntryTuple {
     // https://www.w3.org/TR/performance-timeline/#dfn-performance-entry-buffer
     // A performance entry buffer to store PerformanceEntry objects, that is initially empty.
-    Vector<JS::Handle<PerformanceEntry>> performance_entry_buffer;
+    Vector<JS::NonnullGCPtr<PerformanceEntry>> performance_entry_buffer;
 
     // https://www.w3.org/TR/performance-timeline/#dfn-maxbuffersize
     // An integer maxBufferSize, initialized to the registry value for this entry type.
@@ -45,6 +45,12 @@ struct PerformanceEntryTuple {
         // 4. Return true.
         return true;
     }
+
+    void visit_edges(JS::Cell::Visitor& visitor)
+    {
+        for (auto& entry : performance_entry_buffer)
+            visitor.visit(entry);
+    }
 };
 
 }