Update //third_party/protobuf to version 3.

third_party/protobuf/csharp/src/Google.Protobuf/Reflection/OneofDescriptor.cs

+#region Copyright notice and license
+// Protocol Buffers - Google's data interchange format
+// Copyright 2015 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
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// 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.Collections.Generic;
+using System.Collections.ObjectModel;
+using Google.Protobuf.Compatibility;
+
+namespace Google.Protobuf.Reflection
+{
+    /// <summary>
+    /// Describes a "oneof" field collection in a message type: a set of
+    /// fields of which at most one can be set in any particular message.
+    /// </summary>
+    public sealed class OneofDescriptor : DescriptorBase
+    {
+        private readonly OneofDescriptorProto proto;
+        private MessageDescriptor containingType;
+        private IList<FieldDescriptor> fields;
+        private readonly OneofAccessor accessor;
+
+        internal OneofDescriptor(OneofDescriptorProto proto, FileDescriptor file, MessageDescriptor parent, int index, string clrName)
+            : base(file, file.ComputeFullName(parent, proto.Name), index)
+        {
+            this.proto = proto;
+            containingType = parent;
+
+            file.DescriptorPool.AddSymbol(this);
+            accessor = CreateAccessor(clrName);
+        }
+
+        /// <summary>
+        /// The brief name of the descriptor's target.
+        /// </summary>
+        public override string Name { get { return proto.Name; } }
+
+        /// <summary>
+        /// Gets the message type containing this oneof.
+        /// </summary>
+        /// <value>
+        /// The message type containing this oneof.
+        /// </value>
+        public MessageDescriptor ContainingType
+        {
+            get { return containingType; }
+        }
+
+        /// <summary>
+        /// Gets the fields within this oneof, in declaration order.
+        /// </summary>
+        /// <value>
+        /// The fields within this oneof, in declaration order.
+        /// </value>
+        public IList<FieldDescriptor> Fields { get { return fields; } }
+
+        /// <summary>
+        /// Gets an accessor for reflective access to the values associated with the oneof
+        /// in a particular message.
+        /// </summary>
+        /// <value>
+        /// The accessor used for reflective access.
+        /// </value>
+        public OneofAccessor Accessor { get { return accessor; } }
+
+        internal void CrossLink()
+        {
+            List<FieldDescriptor> fieldCollection = new List<FieldDescriptor>();
+            foreach (var field in ContainingType.Fields.InDeclarationOrder())
+            {
+                if (field.ContainingOneof == this)
+                {
+                    fieldCollection.Add(field);
+                }
+            }
+            fields = new ReadOnlyCollection<FieldDescriptor>(fieldCollection);
+        }
+
+        private OneofAccessor CreateAccessor(string clrName)
+        {
+            var caseProperty = containingType.ClrType.GetProperty(clrName + "Case");
+            if (caseProperty == null)
+            {
+                throw new DescriptorValidationException(this, $"Property {clrName}Case not found in {containingType.ClrType}");
+            }
+            var clearMethod = containingType.ClrType.GetMethod("Clear" + clrName);
+            if (clearMethod == null)
+            {
+                throw new DescriptorValidationException(this, $"Method Clear{clrName} not found in {containingType.ClrType}");
+            }
+
+            return new OneofAccessor(caseProperty, clearMethod, this);
+        }
+    }
+}