Added parsing benchmark.

tests/Avalonia.Benchmarks/Avalonia.Benchmarks.csproj

@@ -1,5 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
+    <OutputType>Exe</OutputType>
     <TargetFrameworks>netcoreapp2.0</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>

tests/Avalonia.Benchmarks/Markup/Parsing.cs

@@ -0,0 +1,34 @@
+using Avalonia.Controls;
+using Avalonia.Markup.Parsers;
+using BenchmarkDotNet.Attributes;
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace Avalonia.Benchmarks.Markup
+{
+    [MemoryDiagnoser]
+    public class Parsing
+    {
+        [Benchmark]
+        public void ParseComplexSelector()
+        {
+            var selectorString = "ListBox > TextBox /template/ TextBlock[IsFocused=True]";
+            var parser = new SelectorParser((ns, s) =>
+            {
+                switch (s)
+                {
+                    case "ListBox":
+                        return typeof(ListBox);
+                    case "TextBox":
+                        return typeof(TextBox);
+                    case "TextBlock":
+                        return typeof(TextBlock);
+                    default:
+                        return null;
+                }
+            });
+            var selector = parser.Parse(selectorString);
+        }
+    }
+}