Add project files.

Compat.Private.Serialization/Compat/Runtime/Serialization/DataContractPairKey.cs

@@ -0,0 +1,30 @@
+namespace Compat.Runtime.Serialization
+{
+    internal class DataContractPairKey
+    {
+        private readonly object _object1;
+        private readonly object _object2;
+
+        public DataContractPairKey(object object1, object object2)
+        {
+            _object1 = object1;
+            _object2 = object2;
+        }
+
+        public override bool Equals(object other)
+        {
+            DataContractPairKey otherKey = other as DataContractPairKey;
+            if (otherKey == null)
+            {
+                return false;
+            }
+
+            return ((otherKey._object1 == _object1 && otherKey._object2 == _object2) || (otherKey._object1 == _object2 && otherKey._object2 == _object1));
+        }
+
+        public override int GetHashCode()
+        {
+            return _object1.GetHashCode() ^ _object2.GetHashCode();
+        }
+    }
+}