Reverts third_party/protobuf: Update to HEAD (f52e188fe4)

third_party/protobuf/csharp/src/Google.Protobuf/Compatibility/TypeExtensions.cs

Index: third_party/protobuf/csharp/src/Google.Protobuf/Compatibility/TypeExtensions.cs
diff --git a/third_party/protobuf/csharp/src/Google.Protobuf/Compatibility/TypeExtensions.cs b/third_party/protobuf/csharp/src/Google.Protobuf/Compatibility/TypeExtensions.cs
index 2d93183b0681b3177700228e48044bab800d8cc3..762a29eb0a3018d8f5d8eb37f83a50326c34d3bf 100644
--- a/third_party/protobuf/csharp/src/Google.Protobuf/Compatibility/TypeExtensions.cs
+++ b/third_party/protobuf/csharp/src/Google.Protobuf/Compatibility/TypeExtensions.cs
@@ -33,7 +33,6 @@
 using System;
 using System.Reflection;
 
-#if !DOTNET35
 namespace Google.Protobuf.Compatibility
 {
     /// <summary>
@@ -47,6 +46,15 @@ namespace Google.Protobuf.Compatibility
     internal static class TypeExtensions
     {
         /// <summary>
+        /// Returns true if the target type is a value type, including a nullable value type or an enum, or false
+        /// if it's a reference type (class, delegate, interface - including System.ValueType and System.Enum).
+        /// </summary>
+        internal static bool IsValueType(this Type target)
+        {
+            return target.GetTypeInfo().IsValueType;
+        }
+
+        /// <summary>
         /// See https://msdn.microsoft.com/en-us/library/system.type.isassignablefrom
         /// </summary>
         internal static bool IsAssignableFrom(this Type target, Type c)
@@ -103,4 +111,3 @@ namespace Google.Protobuf.Compatibility
         }
     }
 }
-#endif