Added some benchmarks

Added some benchmarks to test setting and binding properties.

tests/Avalonia.Benchmarks/Avalonia.Benchmarks.csproj

@@ -49,6 +49,7 @@
     <Reference Include="System.Xml" />
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="Base\Properties.cs" />
     <Compile Include="Layout\Measure.cs" />
     <Compile Include="Styling\ApplyStyling.cs" />
     <Compile Include="Program.cs" />

tests/Avalonia.Benchmarks/Base/Properties.cs

@@ -0,0 +1,43 @@
+using System;
+using System.Reactive.Subjects;
+using BenchmarkDotNet.Attributes;
+
+namespace Avalonia.Benchmarks.Base
+{
+    [MemoryDiagnoser]
+    public class AvaloniaObjectBenchmark
+    {
+        private Class1 target = new Class1();
+        private Subject<int> intBinding = new Subject<int>();
+
+        public AvaloniaObjectBenchmark()
+        {
+            target.SetValue(Class1.IntProperty, 123);
+        }
+
+        [Benchmark]
+        public void ClearAndSetIntProperty()
+        {
+            target.ClearValue(Class1.IntProperty);
+            target.SetValue(Class1.IntProperty, 123);
+        }
+
+        [Benchmark]
+        public void BindIntProperty()
+        {
+            using (target.Bind(Class1.IntProperty, intBinding))
+            {
+                for (var i = 0; i < 100; ++i)
+                {
+                    intBinding.OnNext(i);
+                }
+            }
+        }
+
+        class Class1 : AvaloniaObject
+        {
+            public static readonly AvaloniaProperty<int> IntProperty =
+                AvaloniaProperty.Register<Class1, int>("Int");
+        }
+    }
+}