[System]: System.TimeZoneInfo - implemented GetUtcOffset with DateTimeOffset

mcs/class/corlib/System/TimeZoneInfo.cs

@@ -736,7 +736,8 @@ namespace System
 
 		public TimeSpan GetUtcOffset (DateTimeOffset dateTimeOffset)
 		{
-			throw new NotImplementedException ();
+			bool isDST;
+			return GetUtcOffset (dateTimeOffset.UtcDateTime, out isDST);
 		}
 
 		private TimeSpan GetUtcOffset (DateTime dateTime, out bool isDST)

mcs/class/corlib/Test/System/TimeZoneInfoTest.cs

@@ -1121,7 +1121,33 @@ namespace MonoTests.System
 				Assert.AreEqual(baseUtcOffset, cairo.GetUtcOffset (d));
 				Assert.AreEqual(baseUtcOffset, cairo.GetUtcOffset (d.Add (new TimeSpan(0,0,0, 1))));
 			}
-		}
+
+		  [Test]
+		  public void  GetUtcOffset_FromDateTimeOffset ()
+		  {
+			  DateTimeOffset offset;
+
+			  offset = new DateTimeOffset(dst1Start, baseUtcOffset);
+			  Assert.AreEqual(baseUtcOffset, cairo.GetUtcOffset(offset.Add(new TimeSpan(0, 0, 0, -1))), "dst1Start_with_baseUtcOffset#before");
+			  Assert.AreEqual(dstUtcOffset, cairo.GetUtcOffset(offset), "dst1Start_with_baseUtcOffset#exact");
+			  Assert.AreEqual(dstUtcOffset, cairo.GetUtcOffset(offset.Add(new TimeSpan(0, 0, 0, 1))), "dst1Start_with_baseUtcOffset#after");
+
+			  offset = new DateTimeOffset(dst1End, dstOffset + baseUtcOffset);
+			  Assert.AreEqual(dstUtcOffset, cairo.GetUtcOffset(offset.Add(new TimeSpan(0, 0, 0, -1))), "dst1End_with_dstOffset+baseUtcOffset#before");
+			  Assert.AreEqual(baseUtcOffset, cairo.GetUtcOffset(offset), "dst1End_with_dstOffset+baseUtcOffset#exact");
+			  Assert.AreEqual(baseUtcOffset, cairo.GetUtcOffset(offset.Add(new TimeSpan(0, 0, 0, 1))), "dst1End_with_dstOffset+baseUtcOffset#after");
+
+			  offset = new DateTimeOffset(dst2Start, baseUtcOffset);
+			  Assert.AreEqual(baseUtcOffset, cairo.GetUtcOffset(offset.Add(new TimeSpan(0, 0, 0, -1))), "dst2Start_with_baseUtcOffset#before");
+			  Assert.AreEqual(dstUtcOffset, cairo.GetUtcOffset(offset), "dst2Start_with_baseUtcOffset#exact");
+			  Assert.AreEqual(dstUtcOffset, cairo.GetUtcOffset(offset.Add(new TimeSpan(0, 0, 0, 1))), "dst2Start_with_baseUtcOffset#after");
+
+			  offset = new DateTimeOffset(dst2End, baseUtcOffset + dstOffset);
+			  Assert.AreEqual(dstUtcOffset, cairo.GetUtcOffset(offset.Add(new TimeSpan(0, 0, 0, -1))), "dst2End_with_dstOffset+baseUtcOffset#before");
+			  Assert.AreEqual(baseUtcOffset, cairo.GetUtcOffset(offset), "dst2End_with_dstOffset+baseUtcOffset#exact");
+			  Assert.AreEqual(baseUtcOffset, cairo.GetUtcOffset(offset.Add(new TimeSpan(0, 0, 0, 1))), "dst2End_with_dstOffset+baseUtcOffset#after");
+		  }
+    }
 
 		[TestFixture]
 		public class GetDaylightChanges