test: add tests for ensuring proper timer delays

Includes a passing test that should keep passing and an issue test to
be fixed.

Refs: nodejs#5426
Refs: nodejs#7346
Refs: nodejs#7386

test/known_issues/test-timers-sync-work-delay-problem.js

@@ -0,0 +1,32 @@
+'use strict';
+
+// See https://github.com/nodejs/node/issues/5426
+
+const common = require('../common');
+const TimerWrap = process.binding('timer_wrap').Timer;
+
+function sleep(duration) {
+  var start = Date.now();
+  while ((Date.now() - start) < duration) {
+    for (var i = 0; i < 1e5;) i++;
+  }
+}
+
+var last = TimerWrap.now();
+var count = 0;
+
+const interval = setInterval(common.mustCall(repeat, 4), 500);
+
+function repeat() {
+  if (++count === 4) {
+    clearInterval(interval);
+  }
+  const now = TimerWrap.now();
+
+  if (now < last + 500 - 200 || now > last + 500 + 200) {
+    common.fail(`\`repeat\` delay: ${count} (now: ${now}, last: ${last})\n` +
+                'is not within the margin of error.');
+  }
+  last = now;
+  sleep(500);
+}

test/parallel/test-timers-later-scheduled-delay.js

@@ -0,0 +1,18 @@
+'use strict';
+
+// See https://github.com/nodejs/node/issues/5426#issuecomment-228294811
+
+const common = require('../common');
+const TimerWrap = process.binding('timer_wrap').Timer;
+
+setTimeout(common.mustCall(function first() {}), 1000);
+
+setTimeout(function scheduleLast() {
+  setTimeout(common.mustCall(function last() {
+    const now = TimerWrap.now();
+
+    if (now < 1500 - 200 || now > 1500 + 200) {
+      common.fail('Delay for `last` is not within the margin of error.');
+    }
+  }), 1000);
+}, 500);