Imported Upstream version 6.0.0.172

Former-commit-id: f3cc9b82f3e5bd8f0fd3ebc098f789556b44e9cd

mcs/class/corlib/corefx/CurrentSystemTimeZone.cs

@@ -0,0 +1,52 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+/*============================================================
+**
+**
+**
+** Purpose: 
+** This class represents the current system timezone.  It is
+** the only meaningful implementation of the TimeZone class 
+** available in this version.
+**
+** The only TimeZone that we support in version 1 is the 
+** CurrentTimeZone as determined by the system timezone.
+**
+**
+============================================================*/
+
+using System.Collections;
+using System.Globalization;
+using System.Runtime.Serialization;
+
+namespace System
+{
+    partial class CurrentSystemTimeZone
+    {
+        // copied from CoreRT
+        private DaylightTime GetCachedDaylightChanges(int year)
+        {
+            object objYear = (object)year;
+
+            if (!m_CachedDaylightChanges.Contains(objYear))
+            {
+                DaylightTime currentDaylightChanges = CreateDaylightChanges(year);
+                lock (m_CachedDaylightChanges)
+                {
+                    if (!m_CachedDaylightChanges.Contains(objYear))
+                    {
+                        m_CachedDaylightChanges.Add(objYear, currentDaylightChanges);
+                    }
+                }
+            }
+
+            return (DaylightTime)m_CachedDaylightChanges[objYear];
+        }
+
+        // The per-year information is cached in in this instance value. As a result it can
+        // be cleaned up by CultureInfo.ClearCachedData, which will clear the instance of this object
+        private readonly Hashtable m_CachedDaylightChanges = new Hashtable();
+    } // class CurrentSystemTimeZone
+}