Fixed build issues

src/Avalonia.Controls/DropDown.cs

@@ -120,7 +120,7 @@ namespace Avalonia.Controls
         /// <inheritdoc/>
         protected override void OnPointerPressed(PointerPressedEventArgs e)
         {
-            if (!IsDropDownOpen && ((IVisual)e.Source).GetVisualRoot() != typeof(PopupRoot))
+            if (!IsDropDownOpen && ((IVisual)e.Source).GetVisualRoot() is PopupRoot)
             {
                 IsDropDownOpen = true;
                 e.Handled = true;

src/Avalonia.HtmlRenderer/Compat/Api.cs

@@ -4,18 +4,6 @@ using System.Text;
 
 namespace System.Net
 {
-    internal class AsyncCompletedEventArgs
-    {
-        public object UserState { get; set; }
-        public Exception Error { get; set; }
-        public bool Cancelled { get; set; }
-
-        public AsyncCompletedEventArgs(Exception error, bool cancelled, object userState)
-        {
-
-        }
-    }
-
     class WebException : Exception
     {
         public object Response { get; set; }

src/Markup/Avalonia.Markup.Xaml/Avalonia.Markup.Xaml.csproj

@@ -94,6 +94,7 @@
         <Compile Include="Templates\TemplateLoader.cs" />
         <Compile Include="Templates\TreeDataTemplate.cs" />
         <Compile Include="PortableXaml\portable.xaml.github\src\Portable.Xaml\**\*.cs" Exclude="PortableXaml\portable.xaml.github\src\Portable.Xaml\Assembly\**\*.cs" />
+        <Compile Remove="**\UriTypeConverter.cs" />
     </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\..\Avalonia.Animation\Avalonia.Animation.csproj" />

src/Markup/Avalonia.Markup.Xaml/PortableXaml/portable.xaml.github

@@ -1 +1 @@
-Subproject commit dfc5affa5d8f4ddf5a7707e3202d5593519de640
+Subproject commit eebf9dbb9275ecc48c18ec24f6fbad8cb494857f

src/Shared/PlatformSupport/StandardRuntimePlatform.cs

@@ -12,7 +12,7 @@ namespace Avalonia.Shared.PlatformSupport
     internal partial class StandardRuntimePlatform : IRuntimePlatform
     {
 
-#if NETCOREAPP1_0
+#if NETCOREAPP2_0
         public void PostThreadPoolItem(Action cb) =>  ThreadPool.QueueUserWorkItem(_ => cb(), null);
 #else
         public Assembly[] GetLoadedAssemblies() => AppDomain.CurrentDomain.GetAssemblies();

src/Windows/Avalonia.Win32/Interop/UnmanagedMethods.cs

@@ -811,7 +811,7 @@ namespace Avalonia.Win32.Interop
 
             return SetClassLong64(hWnd, nIndex, dwNewLong);
         }
-#if !NETSTANDARD && !NETSTANDARD1_3
+#if !NETSTANDARD && !NETSTANDARD2_0
         [ComImport, ClassInterface(ClassInterfaceType.None), TypeLibType(TypeLibTypeFlags.FCanCreate), Guid("DC1C5A9C-E88A-4DDE-A5A1-60F82A20AEF7")]
         internal class FileOpenDialogRCW { }