Remove RequiredPolicy

[HaoK]

Fixes #9398

[pranavkm]

Formatting.

[pranavkm]

@rynowak \ @JamesNK can we have GetOrderedMetadata return an IReadOnlyList<T>? It internally caches an T[] so there isn't any code change involved with it.

[pranavkm]

@Eilon, @rynowak pointed out that this would be a breaking change since the API exists in 2.2. However, this seems like a worthwhile change to make - other APIs and users are likely to benefit from this change. How do you feel about this change?

[pranavkm]

We could just do Count() here. It'll effectively be the same: https://github.com/dotnet/corefx/blob/master/src/System.Linq/src/System/Linq/Count.cs#L12-L22

[HaoK]

@pranavkm test failure which doesn't look related to this change, is this a known issue? Should I just retry?

   at System.Net.Http.HttpContent.LoadIntoBufferAsyncCore(Task serializeToStreamTask, MemoryStream tempBuffer)
   at System.Net.Http.HttpClient.FinishSendAsyncBuffered(Task`1 sendTask, HttpRequestMessage request, CancellationTokenSource cts, Boolean disposeCts)
   at Microsoft.AspNetCore.Mvc.FunctionalTests.HttpClientExtensions.GetHtmlDocumentAsync(HttpClient client, String requestUri) in /_/src/Mvc/test/Mvc.FunctionalTests/Infrastructure/HttpClientExtensions.cs:line 18
   at Microsoft.AspNetCore.Mvc.FunctionalTests.FlushPointTest.FlushFollowedByLargeContent() in /_/src/Mvc/test/Mvc.FunctionalTests/FlushPointTest.cs:line 45
--- End of stack trace from previous location where exception was thrown ---
----- Inner Stack Trace -----
   at System.IO.Pipelines.PipeCompletion.ThrowLatchedException()
   at System.IO.Pipelines.Pipe.GetReadResult(ReadResult& result)
   at System.IO.Pipelines.Pipe.GetReadAsyncResult()
   at Microsoft.AspNetCore.TestHost.ResponseStream.ReadAsync(Byte[] buffer, Int32 offset, Int32 count, CancellationToken cancellationToken) in /_/src/Hosting/TestHost/src/ResponseStream.cs:line 114
   at System.IO.Stream.CopyToAsyncInternal(Stream destination, Int32 bufferSize, CancellationToken cancellationToken)
   at System.Net.Http.StreamToStreamCopy.<>c.<DisposeSourceWhenCompleteAsync>b__1_0(Task completed, Object innerSource)
   at System.Threading.Tasks.ContinuationTaskFromTask.InnerInvoke()
   at System.Threading.Tasks.Task.<>c.<.cctor>b__274_0(Object obj)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
--- End of stack trace from previous location where exception was thrown ---
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.Tasks.Task.ExecuteWithThreadLocal(Task& currentTaskSlot, Thread threadPoolThread)
--- End of stack trace from previous location where exception was thrown ---
   at System.Net.Http.HttpContent.LoadIntoBufferAsyncCore(Task serializeToStreamTask, MemoryStream tempBuffer)
----- Inner Stack Trace -----

[pranavkm]

@aspnet-hello triage https://dev.azure.com/dnceng/public/_build/results?buildId=159145

[pranavkm]

Yeah, I kicked off a retry. It's a fairly new test, so perhaps there's a bug :(

[aspnet-hello]

This comment was made automatically. If there is a problem contact ryanbrandenburg.

I've triaged the above build. I've created/commented on the following issue(s)
https://github.com/aspnet/AspNetCore-Internal/issues/2300