Add MergeFrom Methods to MapField for Dictionary and MapField Merging

Runtime/Google.Protobuf/Collections/MapField.cs

@@ -81,6 +81,32 @@ public sealed class MapField<TKey, TValue> : IDeepCloneable<MapField<TKey, TValu
             new Dictionary<TKey, LinkedListNode<KeyValuePair<TKey, TValue>>>(KeyEqualityComparer);
         private readonly LinkedList<KeyValuePair<TKey, TValue>> list = new LinkedList<KeyValuePair<TKey, TValue>>();
 
+        /// <summary>
+        /// Merges entries from an <see cref="IDictionary{TKey, TValue}"/> into this instance.
+        /// </summary>
+        /// <param name="other">
+        /// The dictionary whose entries will be merged into this map.
+        /// </param>
+        public void MergeFrom(IDictionary<TKey, TValue> other)
+        {
+            foreach (var kv in other)
+            {
+                this[kv.Key] = kv.Value;
+            }
+        }
+
+        /// <summary>
+        /// Merges entries from another <see cref="MapField{TKey, TValue}"/> into this instance.
+        /// </summary>
+        /// <param name="other">
+        /// The <see cref="MapField{TKey, TValue}"/> whose entries will be merged.
+        /// </param>
+        public void MergeFrom(MapField<TKey, TValue> other)
+        {
+            // Reuse the IDictionary<TKey, TValue> MergeFrom implementation
+            MergeFrom((IDictionary<TKey, TValue>)other);
+        }
+
         /// <summary>
         /// Creates a deep clone of this object.
         /// </summary>