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

third_party/protobuf/csharp/protos/unittest_issues.proto

Index: third_party/protobuf/csharp/protos/unittest_issues.proto
diff --git a/third_party/protobuf/csharp/protos/unittest_issues.proto b/third_party/protobuf/csharp/protos/unittest_issues.proto
index 989b3dc426e9c678bef641b3251f9b125765f74a..6c9f76344abe951d85e81437ac68500a2811af15 100644
--- a/third_party/protobuf/csharp/protos/unittest_issues.proto
+++ b/third_party/protobuf/csharp/protos/unittest_issues.proto
@@ -116,4 +116,11 @@ message TestJsonFieldOrdering {
     string o2_string = 3;
   }
   
-}
+}
+
+message TestJsonName {
+  // Message for testing the effects for of the json_name option
+  string name = 1;
+  string description = 2 [json_name = "desc"];
+  string guid = 3 [json_name = "exid"];
+}