Add Lazy<T>(T value) constructor

src/System.Private.CoreLib/src/System/Lazy.cs

@@ -124,6 +124,19 @@ public Lazy(Func<T> valueFactory)
         {
         }
 
+        /// <summary>
+        /// Initializes a new instance of the <see cref="T:System.Threading.Lazy{T}"/> class that
+        /// uses a pre-initialized specified value.
+        /// </summary>
+        /// <remarks>
+        /// An instance created with this constructor should be usable by multiple threads
+        //  concurrently.
+        /// </remarks>
+        public Lazy(T value)
+        {
+            _boxed = new Boxed(value);
+        }
+
         /// <summary>
         /// Initializes a new instance of the <see cref="T:System.Threading.Lazy{T}"/>
         /// class that uses <typeparamref name="T"/>'s default constructor and a specified thread-safety mode.