Remove unused WinHttpHandler.MaxRequestContentBufferSize property

This property has been effectively deprecated. It was left unimplemented in WinHttpHandler until we realized that we should remove it from the public WinHttpHandler contract.

In the .NET Desktop, the equivalent HttpClientHandler.MaxRequestContentBufferSize property was only used when the handler needed to automatically buffer the request content. That only happened if neither 'Content-Length' nor 'Transfer-Encoding: chunked' request headers were specified. The advice to developers is to always be precise with the headers and explicitly choose the transfer mechanism. So, this condition is an edge case.

When left ambiguous, the handler thus needed to buffer in the request content to determine its length and then would choose 'Content-Length' semantics when POST'ing.

In CoreCLR and .NETNative, the handler will resolve the ambiguity by always choosing 'Transfer-Encoding: chunked'. The handler will never automatically buffer in the request content.

[tfs-changeset: 1492780]

Author: davidsh

src/System.Net.Http/src/System/Net/HttpClientHandler.CoreCLR.cs

@@ -121,8 +121,16 @@ public int MaxAutomaticRedirections
 
         public long MaxRequestContentBufferSize
         {
-            get { return _winHttpHandler.MaxRequestContentBufferSize; }
-            set { _winHttpHandler.MaxRequestContentBufferSize = value; }
+            // This property has been deprecated. In the .NET Desktop it was only used when the handler needed to automatically
+            // buffer the request content. That only happened if neither 'Content-Length' nor 'Transfer-Encoding: chunked'
+            // request headers were specified. So, the handler thus needed to buffer in the request content to determine its
+            // length and then would choose 'Content-Length' semantics when POST'ing. In CoreCLR and .NETNative, the handler
+            // will resolve the ambiguity by always choosing 'Transfer-Encoding: chunked'. The handler will never automatically
+            // buffer in the request content.
+            get { return 0; }
+            
+            // TODO: Add message/link to exception explaining the deprecation.
+            set { throw new PlatformNotSupportedException(); }
         }
 
         #endregion Properties