Update //third_party/protobuf to version 3.

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();
+        }
+    }
+}