third_party/protobuf: Update to HEAD (f52e188fe4)

third_party/protobuf/csharp/src/Google.Protobuf.Test/ByteStringTest.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 149 matching lines @@
             ByteString bs = ByteString.FromBase64(base64);
             Assert.AreEqual(data, bs.ToByteArray());
         }
 
         [Test]
         public void FromBase64_Empty()
         {
             // Optimization which also fixes issue 61.
             Assert.AreSame(ByteString.Empty, ByteString.FromBase64(""));
         }
+
+        [Test]
+        public void GetHashCode_Regression()
+        {
+            // We used to have an awful hash algorithm where only the last four
+            // bytes were relevant. This is a regression test for
+            // https://github.com/google/protobuf/issues/2511
+
+            ByteString b1 = ByteString.CopyFrom(100, 1, 2, 3, 4);
+            ByteString b2 = ByteString.CopyFrom(200, 1, 2, 3, 4);
+            Assert.AreNotEqual(b1.GetHashCode(), b2.GetHashCode());
+        }
+
     }
 }