Update //third_party/protobuf to version 3.

third_party/protobuf/csharp/src/Google.Protobuf/Reflection/DescriptorBase.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
+// 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
+
+namespace Google.Protobuf.Reflection
+{
+    /// <summary>
+    /// Base class for nearly all descriptors, providing common functionality.
+    /// </summary>
+    public abstract class DescriptorBase : IDescriptor
+    {
+        private readonly FileDescriptor file;
+        private readonly string fullName;
+        private readonly int index;
+
+        internal DescriptorBase(FileDescriptor file, string fullName, int index)
+        {
+            this.file = file;
+            this.fullName = fullName;
+            this.index = index;
+        }
+
+        /// <value>
+        /// The index of this descriptor within its parent descriptor. 
+        /// </value>
+        /// <remarks>
+        /// This returns the index of this descriptor within its parent, for
+        /// this descriptor's type. (There can be duplicate values for different
+        /// types, e.g. one enum type with index 0 and one message type with index 0.)
+        /// </remarks>
+        public int Index
+        {
+            get { return index; }
+        }
+
+        /// <summary>
+        /// Returns the name of the entity (field, message etc) being described.
+        /// </summary>
+        public abstract string Name { get; }
+
+        /// <summary>
+        /// The fully qualified name of the descriptor's target.
+        /// </summary>
+        public string FullName
+        {
+            get { return fullName; }
+        }
+
+        /// <value>
+        /// The file this descriptor was declared in.
+        /// </value>
+        public FileDescriptor File
+        {
+            get { return file; }
+        }
+    }
+}