Add sample for 'repeat' function

Co-authored-by: Ilya Gorbunov <ilya.gorbunov@jetbrains.com>

libraries/stdlib/samples/test/samples/misc/controlFlow.kt

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+package samples.misc
+
+import samples.*
+
+class ControlFlow {
+
+    @Sample
+    fun repeat() {
+        // greets three times
+        repeat(3) {
+            println("Hello")
+        }
+
+        repeat(0) {
+            error("We should not get here!")
+        }
+    }
+}

libraries/stdlib/src/kotlin/util/Standard.kt

@@ -128,6 +128,8 @@ public inline fun <T> T.takeUnless(predicate: (T) -> Boolean): T? {
  * Executes the given function [action] specified number of [times].
  *
  * A zero-based index of current iteration is passed as a parameter to [action].
+ *
+ * @sample samples.misc.ControlFlow.repeat
  */
 @kotlin.internal.InlineOnly
 public inline fun repeat(times: Int, action: (Int) -> Unit) {