Add RuntimeHelpers.GetUninitializedObject for netcoreapp1.1

src/System.Runtime/ref/System.Runtime.cs

@@ -5668,6 +5668,7 @@ public static void PrepareMethod(System.RuntimeMethodHandle method, System.Runti
         public static void ProbeForSufficientStack() { }
 #if netcoreapp11
         public static bool TryEnsureSufficientExecutionStack() { return default(bool); }
+        public static object GetUninitializedObject(Type type) { return default(object); }
 #endif
    }
    [System.AttributeUsageAttribute((System.AttributeTargets)(64), Inherited = false, AllowMultiple = false)]

src/System.Runtime/tests/System/Runtime/CompilerServices/RuntimeHelpersTests.netcoreapp1.1.cs

@@ -36,5 +36,35 @@ private static void FillStack(int depth)
                 FillStack(depth + 1);
             } 
         }
+
+        [Fact]
+        public static void GetUninitializedObject_InvalidArguments_ThrowsException()
+        {
+            Assert.Throws<ArgumentNullException>("type", () => RuntimeHelpers.GetUninitializedObject(null));
+
+            Assert.Throws<ArgumentException>(() => RuntimeHelpers.GetUninitializedObject(typeof(string))); // special type
+            Assert.Throws<MemberAccessException>(() => RuntimeHelpers.GetUninitializedObject(typeof(System.IO.Stream))); // abstract type
+            Assert.Throws<MemberAccessException>(() => RuntimeHelpers.GetUninitializedObject(typeof(System.Collections.IEnumerable))); // interface
+            Assert.Throws<MemberAccessException>(() => RuntimeHelpers.GetUninitializedObject(typeof(System.Collections.Generic.List<>))); // generic definition
+        }
+
+        [Fact]
+        public static void GetUninitializedObject_DoesNotRunConstructor()
+        {
+            Assert.Equal(42, new ObjectWithDefaultCtor().Value);
+            Assert.Equal(0, ((ObjectWithDefaultCtor)RuntimeHelpers.GetUninitializedObject(typeof(ObjectWithDefaultCtor))).Value);
+        }
+
+        [Fact]
+        public static void GetUninitializedObject_Nullable()
+        {
+            // Nullable returns the underlying type instead
+            Assert.Equal(typeof(int), RuntimeHelpers.GetUninitializedObject(typeof(Nullable<int>)).GetType());
+        }
+
+        private class ObjectWithDefaultCtor
+        {
+            public int Value = 42;
+        }
     }
 }