TryAddWithoutValidation for multiple values could be more efficient

src/benchmarks/micro/libraries/System.Net.Http/HttpHeaders.cs

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+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using BenchmarkDotNet.Attributes;
+using BenchmarkDotNet.Engines;
+using MicroBenchmarks;
+using System.Collections.Generic;
+using System.Linq;
+using System.Net.Http;
+using System.Net.Http.Headers;
+
+namespace System.Net.Http.Tests
+{
+    [BenchmarkCategory(Categories.Libraries)]
+    public class HttpHeaders
+    {
+        private readonly HttpResponseHeaders _responseHeaders = new HttpResponseMessage().Headers;
+
+        [Benchmark]
+        [ArgumentsSource(nameof(IEnumerableArgument))]
+        public bool TryAddWithoutValidationTests(TryAddWithoutValidationTestData data)
+        {
+            var result = _responseHeaders.TryAddWithoutValidation("headerName", data.Values);
+            _responseHeaders.Clear();
+            return result;
+        }
+
+        public IEnumerable<TryAddWithoutValidationTestData> IEnumerableArgument()
+        {
+            yield return new TryAddWithoutValidationTestData("Array", Enumerable.Range(0, 5).Select(i => "value" + i).ToArray()); // tests IList optimized case
+            yield return new TryAddWithoutValidationTestData("List", Enumerable.Range(0, 5).Select(i => "value" + i).ToList()); // tests IList optimized case
+            yield return new TryAddWithoutValidationTestData("Hashset", new HashSet<string>(Enumerable.Range(0, 5).Select(i => "value" + i))); // tests the slow path IEnumerable case
+        }
+    }
+
+    public class TryAddWithoutValidationTestData
+    {
+        public IEnumerable<string> Values { get; }
+
+        public string InstanceName { get; }
+
+        public TryAddWithoutValidationTestData(string instanceName, IEnumerable<string> values)
+        {
+            InstanceName = instanceName;
+            Values = values;
+        }
+
+        public override string ToString() => InstanceName;
+    }
+}