Added samples for the kotlin.system package (measureTime* functions)

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

libraries/stdlib/jvm/src/kotlin/system/Timing.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2018 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
@@ -10,6 +10,8 @@ import kotlin.contracts.*
 
 /**
  * Executes the given [block] and returns elapsed time in milliseconds.
+ *
+ * @sample samples.system.Timing.measureBlockTimeMillis
  */
 public inline fun measureTimeMillis(block: () -> Unit): Long {
     contract {
@@ -22,6 +24,8 @@ public inline fun measureTimeMillis(block: () -> Unit): Long {
 
 /**
  * Executes the given [block] and returns elapsed time in nanoseconds.
+ *
+ * @sample samples.system.Timing.measureBlockNanoTime
  */
 public inline fun measureNanoTime(block: () -> Unit): Long {
     contract {

libraries/stdlib/samples/test/samples/system/timing.kt

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * 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.system
+
+import samples.*
+import kotlin.system.*
+
+class Timing {
+
+    @Sample
+    fun measureBlockTimeMillis() {
+        val numbers: List<Int>
+        val timeInMillis = measureTimeMillis {
+            numbers = buildList {
+                addAll(0..100)
+                shuffle()
+                sortDescending()
+            }
+        }
+        // here numbers are initialized and sorted
+        assertPrints(numbers.first(), "100")
+
+        println("(The operation took $timeInMillis ms)")
+    }
+
+    @Sample
+    fun measureBlockNanoTime() {
+        var sqrt = 0
+        val number = 1000
+        val timeInNanos = measureNanoTime {
+            while (sqrt * sqrt < number) sqrt++
+        }
+        println("(The operation took $timeInNanos ns)")
+        println("The approximate square root of $number is between ${sqrt - 1} and $sqrt")
+    }
+}