Custom new HttpClientHandler() when HttpSymbolServer is built on .netstandard

Author: ladeak

src/Microsoft.SymbolStore/SymbolStores/HttpSymbolStore.cs

@@ -67,7 +67,15 @@ public HttpSymbolStore(ITracer tracer, SymbolStore backingStore, Uri symbolServe
             _authenticationFunc = authenticationFunc;
 
             // Create client
-            _client = new HttpClient
+#if NETSTANDARD2_0
+            _client = new HttpClient(new HttpClientHandler()
+            {
+                UseProxy = true,
+                DefaultProxyCredentials = CredentialCache.DefaultNetworkCredentials,
+            })
+#else
+            _client = new HttpClient()
+#endif
             {
                 Timeout = TimeSpan.FromMinutes(4)
             };

src/Tools/dotnet-dump/Analyzer.cs

@@ -104,7 +104,6 @@ or NotSupportedException
                 contextService.SetCurrentTarget(target);
 
                 // Automatically enable symbol server support, default cache and search for symbols in the dump directory
-                HttpClient.DefaultProxy.Credentials = CredentialCache.DefaultCredentials;
                 symbolService.AddSymbolServer(retryCount: 3);
                 symbolService.AddCachePath(symbolService.DefaultSymbolCache);
                 symbolService.AddDirectoryPath(Path.GetDirectoryName(dump_path.FullName));

src/Tools/dotnet-symbol/Program.cs

@@ -265,7 +265,6 @@ internal async Task DownloadFiles()
         private Microsoft.SymbolStore.SymbolStores.SymbolStore BuildSymbolStore()
         {
             Microsoft.SymbolStore.SymbolStores.SymbolStore store = null;
-            HttpClient.DefaultProxy.Credentials = CredentialCache.DefaultCredentials;
             foreach (ServerInfo server in ((IEnumerable<ServerInfo>)SymbolServers).Reverse())
             {
                 if (server.InternalSymwebServer)