Update third_party/protobuf to protobuf-v3.0.0-beta-3

third_party/protobuf/csharp/src/Google.Protobuf/ProtoPreconditions.cs

 #region Copyright notice and license
 // Protocol Buffers - Google's data interchange format
 // Copyright 2008 Google Inc.  All rights reserved.
 // https://developers.google.com/protocol-buffers/
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
@@ skipping 17 matching lines @@
 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #endregion
 
 using System;
 
 namespace Google.Protobuf
 {
     /// <summary>
-    /// Helper methods for throwing exceptions
+    /// Helper methods for throwing exceptions when preconditions are not met.
     /// </summary>
-    public static class Preconditions
+    /// <remarks>
+    /// This class is used internally and by generated code; it is not particularly
+    /// expected to be used from application code, although nothing prevents it
+    /// from being used that way.
+    /// </remarks>
+    public static class ProtoPreconditions
     {
         /// <summary>
         /// Throws an ArgumentNullException if the given value is null, otherwise
         /// return the value to the caller.
         /// </summary>
         public static T CheckNotNull<T>(T value, string name) where T : class
         {
             if (value == null)
             {
                 throw new ArgumentNullException(name);
@@ skipping 14 matching lines @@
         internal static T CheckNotNullUnconstrained<T>(T value, string name)
         {
             if (value == null)
             {
                 throw new ArgumentNullException(name);
             }
             return value;
         }
     }
 }