Add shouldBeNow() to js-tests.js in LayoutTests.

LayoutTests/resources/js-test.js

Index: LayoutTests/resources/js-test.js
diff --git a/LayoutTests/resources/js-test.js b/LayoutTests/resources/js-test.js
index 5909e86f6f3ba056753d1c7f6d81cd464958830d..5799d52ad09ad7696234e3ed10f049566f281db1 100644
--- a/LayoutTests/resources/js-test.js
+++ b/LayoutTests/resources/js-test.js
@@ -569,6 +569,39 @@ function shouldThrow(_a, _e)
     testFailed(_a + " should throw " + (typeof _e == "undefined" ? "an exception" : _ev) + ". Was " + _av + ".");
 }
 
+function shouldBeNow(_a)
+{
+    for (var _i = 0; _i < 1000; ++_i) {

[ojan, 2013/11/23 01:41:31]

No need for the underscores. jsbell has a patch removing the other underscore
prefixes from this file.

[pwnall-personal, 2013/11/23 01:56:22]

Done.

+        var _startDate = Date.now();
+        var _av = eval(_a);
+        var _date = _av.valueOf();
+        var _endDate = Date.now();
+
+        // On some occasions such as NTP updates, the current time can go
+        // backwards. This should only happen rarely, so we can get away with
+        // retrying the test a few times if we detect the time going backwards.
+        if (_startDate > _endDate)
+            continue;
+
+        if (typeof _date !== "number") {
+            testFailed(_a + " is not a number or a Date. Got " + _av);
+            return;
+        }
+        if (_date < _startDate) {
+            testFailed(_a + " is not the curent time. Got " + _av + " which is " + (_startDate - _date) / 1000 + " seconds in the past.");
+            return;
+        }
+        if (_date > _endDate) {
+            testFailed(_a + " is not the current time. Got " + _av + " which is " + (_date - _endDate) / 1000 + " seconds in the future.");
+            return;
+        }
+
+        testPassed(_a + " is equivalent to Date.now().");
+        return;
+    }
+    testFailed(_a + " cannot be tested against the current time. The clock is going backwards too often.");
+}
+
 function expectError()
 {
     if (expectingError) {