Remove pragma warning disable 1998

Function doesn't need async

src/Microsoft.AspNetCore.Razor.Runtime/Internal/TaskCache.cs

@@ -0,0 +1,24 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.Threading.Tasks;
+
+namespace Microsoft.AspNetCore.Razor.Internal
+{
+    public static class TaskCache
+    {
+
+        /// <summary>
+        /// A <see cref="Task"/> that's already completed successfully.
+        /// </summary>
+        /// <remarks>
+        /// We're caching this in a static readonly field to make it more inlinable and avoid the volatile lookup done
+        /// by <c>Task.CompletedTask</c>.
+        /// </remarks>
+#if NET451
+        public static readonly Task CompletedTask = Task.FromResult(0);
+#else
+        public static readonly Task CompletedTask = Task.CompletedTask;
+#endif
+    }
+}

src/Microsoft.AspNetCore.Razor.Runtime/Runtime/TagHelpers/TagHelperExecutionContext.cs

@@ -6,6 +6,7 @@ using System.Collections.Generic;
 using System.Diagnostics;
 using System.Text.Encodings.Web;
 using System.Threading.Tasks;
+using Microsoft.AspNetCore.Razor.Internal;
 using Microsoft.AspNetCore.Razor.TagHelpers;
 
 namespace Microsoft.AspNetCore.Razor.Runtime.TagHelpers
@@ -31,7 +32,7 @@ namespace Microsoft.AspNetCore.Razor.Runtime.TagHelpers
                    tagMode,
                    items: new Dictionary<object, object>(),
                    uniqueId: string.Empty,
-                   executeChildContentAsync: async () => await Task.FromResult(result: true),
+                   executeChildContentAsync: () => TaskCache.CompletedTask,
                    startTagHelperWritingScope: _ => { },
                    endTagHelperWritingScope: () => new DefaultTagHelperContent())
         {

src/Microsoft.AspNetCore.Razor.Runtime/TagHelpers/TagHelper.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System.Threading.Tasks;
+using Microsoft.AspNetCore.Razor.Internal;
 
 namespace Microsoft.AspNetCore.Razor.TagHelpers
 {
@@ -37,11 +38,10 @@ namespace Microsoft.AspNetCore.Razor.TagHelpers
         /// <param name="output">A stateful HTML element used to generate an HTML tag.</param>
         /// <returns>A <see cref="Task"/> that on completion updates the <paramref name="output"/>.</returns>
         /// <remarks>By default this calls into <see cref="Process"/>.</remarks>.
-#pragma warning disable 1998
-        public virtual async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
+        public virtual Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
         {
             Process(context, output);
+            return TaskCache.CompletedTask;
         }
-#pragma warning restore 1998
     }
 }