dont use generic version of Marshal.SizeOf

src/csharp/Grpc.Core.Tests/Internal/CompletionQueueEventTest.cs

@@ -29,9 +29,12 @@ namespace Grpc.Core.Internal.Tests
     public class CompletionQueueEventTest
     {
         [Test]
-        public void CreateAndDestroy()
+        public void CompletionQueueEventSizeIsNativeSize()
         {
-            Assert.AreEqual(CompletionQueueEvent.NativeSize, Marshal.SizeOf<CompletionQueueEvent>());
+            #pragma warning disable 0618
+            // We need to use the obsolete non-generic version of Marshal.SizeOf because the generic version is not available in net45
+            Assert.AreEqual(CompletionQueueEvent.NativeSize, Marshal.SizeOf(typeof(CompletionQueueEvent)));
+            #pragma warning restore 0618
         }
     }
 }

src/csharp/Grpc.Core.Tests/Internal/TimespecTest.cs

@@ -60,7 +60,10 @@ namespace Grpc.Core.Internal.Tests
         [Test]
         public void TimespecSizeIsNativeSize()
         {
-            Assert.AreEqual(Timespec.NativeSize, Marshal.SizeOf<Timespec>());
+            #pragma warning disable 0618
+            // We need to use the obsolete non-generic version of Marshal.SizeOf because the generic version is not available in net45
+            Assert.AreEqual(Timespec.NativeSize, Marshal.SizeOf(typeof(Timespec)));
+            #pragma warning restore 0618
         }
 
         [Test]

src/csharp/Grpc.Core/Internal/AuthContextSafeHandle.cs

@@ -75,8 +75,7 @@ namespace Grpc.Core.Internal
         private AuthProperty PtrToAuthProperty(IntPtr authPropertyPtr)
         {
             #pragma warning disable 0618
-            // We need to use the obsolete non-generic version of Marshal.PtrToStructure, because the generic version is not available
+            // We need to use the obsolete non-generic version of Marshal.PtrToStructure, because the generic version is not available in net45
-            // in net45 on Windows.
             var nativeAuthProperty = (NativeAuthProperty) Marshal.PtrToStructure(authPropertyPtr, typeof(NativeAuthProperty));
             #pragma warning restore 0618
             var name = Marshal.PtrToStringAnsi(nativeAuthProperty.Name);