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

third_party/protobuf/csharp/src/Google.Protobuf/Collections/ReadOnlyDictionary.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
-
-using System;
-using System.Collections;
-using System.Collections.Generic;
-
-namespace Google.Protobuf.Collections
-{
-    /// <summary>
-    /// Read-only wrapper around another dictionary.
-    /// </summary>
-    internal sealed class ReadOnlyDictionary<TKey, TValue> : IDictionary<TKey, TValue>
-    {
-        private readonly IDictionary<TKey, TValue> wrapped;
-
-        public ReadOnlyDictionary(IDictionary<TKey, TValue> wrapped)
-        {
-            this.wrapped = wrapped;
-        }
-
-        public void Add(TKey key, TValue value)
-        {
-            throw new InvalidOperationException();
-        }
-
-        public bool ContainsKey(TKey key)
-        {
-            return wrapped.ContainsKey(key);
-        }
-
-        public ICollection<TKey> Keys
-        {
-            get { return wrapped.Keys; }
-        }
-
-        public bool Remove(TKey key)
-        {
-            throw new InvalidOperationException();
-        }
-
-        public bool TryGetValue(TKey key, out TValue value)
-        {
-            return wrapped.TryGetValue(key, out value);
-        }
-
-        public ICollection<TValue> Values
-        {
-            get { return wrapped.Values; }
-        }
-
-        public TValue this[TKey key]
-        {
-            get { return wrapped[key]; }
-            set { throw new InvalidOperationException(); }
-        }
-
-        public void Add(KeyValuePair<TKey, TValue> item)
-        {
-            throw new InvalidOperationException();
-        }
-
-        public void Clear()
-        {
-            throw new InvalidOperationException();
-        }
-
-        public bool Contains(KeyValuePair<TKey, TValue> item)
-        {
-            return wrapped.Contains(item);
-        }
-
-        public void CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex)
-        {
-            wrapped.CopyTo(array, arrayIndex);
-        }
-
-        public int Count
-        {
-            get { return wrapped.Count; }
-        }
-
-        public bool IsReadOnly
-        {
-            get { return true; }
-        }
-
-        public bool Remove(KeyValuePair<TKey, TValue> item)
-        {
-            throw new InvalidOperationException();
-        }
-
-        public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()
-        {
-            return wrapped.GetEnumerator();
-        }
-
-        IEnumerator IEnumerable.GetEnumerator()
-        {
-            return ((IEnumerable) wrapped).GetEnumerator();
-        }
-
-        public override bool Equals(object obj)
-        {
-            return wrapped.Equals(obj);
-        }
-
-        public override int GetHashCode()
-        {
-            return wrapped.GetHashCode();
-        }
-
-        public override string ToString()
-        {
-            return wrapped.ToString();
-        }
-    }
-}