Added performance test for converting images

Html2Amp.PerfTests/Html2Amp.PerfTests.csproj

@@ -52,6 +52,7 @@
   </ItemGroup>
   <ItemGroup>
     <Compile Include="ElementExtensionsTests\ElementExtensions_CopyTo.cs" />
+    <Compile Include="Html2AmpConverting\ConvertingImageElement.cs" />
     <Compile Include="Program.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
   </ItemGroup>

Html2Amp.PerfTests/Html2AmpConverting/ConvertingImageElement.cs

@@ -0,0 +1,20 @@
+using BenchmarkDotNet.Attributes;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Html2Amp.PerfTests
+{
+	public class HtmlConverting
+	{
+		private static HtmlToAmpConverter htmlToAmpConverter = new HtmlToAmpConverter();
+
+		[Benchmark]
+		public ConvertionResult ConvertSimpleImageElementToAmp()
+		{
+			return htmlToAmpConverter.ConvertFromHtml("<img src=\"test-image.png\" width=\"100\" height=\"100\" />");
+		}
+	}
+}

Html2Amp.PerfTests/Program.cs

@@ -13,6 +13,7 @@ public class Program
 		public static void Main(string[] args)
 		{
 			BenchmarkRunner.Run<ElementExtensions_CopyTo>();
+			BenchmarkRunner.Run<HtmlConverting>();
 		}
 	}
 }