Reverts third_party/protobuf: Update to HEAD (f52e188fe4)

third_party/protobuf/csharp/src/Google.Protobuf.Test/Compatibility/TypeExtensionsTest.cs

Index: third_party/protobuf/csharp/src/Google.Protobuf.Test/Compatibility/TypeExtensionsTest.cs
diff --git a/third_party/protobuf/csharp/src/Google.Protobuf.Test/Compatibility/TypeExtensionsTest.cs b/third_party/protobuf/csharp/src/Google.Protobuf.Test/Compatibility/TypeExtensionsTest.cs
index f430b06beda3cc0ffc7477abde068a1634a1f4d5..f0c8d3bcc6e3d194b9a3fac124ae507773501d56 100644
--- a/third_party/protobuf/csharp/src/Google.Protobuf.Test/Compatibility/TypeExtensionsTest.cs
+++ b/third_party/protobuf/csharp/src/Google.Protobuf.Test/Compatibility/TypeExtensionsTest.cs
@@ -34,7 +34,6 @@ using System;
 using System.Collections.Generic;
 using System.Reflection;
 
-#if !DOTNET35
 namespace Google.Protobuf.Compatibility
 {
     public class TypeExtensionsTest
@@ -52,6 +51,24 @@ namespace Google.Protobuf.Compatibility
         }
 
         [Test]
+        [TestCase(typeof(int), true)]
+        [TestCase(typeof(int?), true)]
+        [TestCase(typeof(Nullable<>), true)]
+        [TestCase(typeof(WireFormat.WireType), true)]
+        [TestCase(typeof(string), false)]
+        [TestCase(typeof(object), false)]
+        [TestCase(typeof(Enum), false)]
+        [TestCase(typeof(ValueType), false)]
+        [TestCase(typeof(TypeExtensionsTest), false)]
+        [TestCase(typeof(Action), false)]
+        [TestCase(typeof(Action<>), false)]
+        [TestCase(typeof(IDisposable), false)]
+        public void IsValueType(Type type, bool expected)
+        {
+            Assert.AreEqual(expected, TypeExtensions.IsValueType(type));
+        }
+
+        [Test]
         [TestCase(typeof(object), typeof(string), true)]
         [TestCase(typeof(object), typeof(int), true)]
         [TestCase(typeof(string), typeof(string), true)]
@@ -114,4 +131,3 @@ namespace Google.Protobuf.Compatibility
         }
     }
 }
-#endif