Revert https://codereview.chromium.org/1291903002 (protobuf roll).

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; }
-        }
-    }
-}