Add performance.now() to the d8 shell.

test/mjsunit/d8-performance-now.js

Index: test/mjsunit/d8-performance-now.js
diff --git a/test/mjsunit/regress/regress-grow-store-smi-check.js b/test/mjsunit/d8-performance-now.js
similarity index 63%
copy from test/mjsunit/regress/regress-grow-store-smi-check.js
copy to test/mjsunit/d8-performance-now.js
index 381141d52317c22cf19547a3626280fa2cb1ba9b..759fed3054bef8281c96c0ec929f4a7aab3dd94b 100644
--- a/test/mjsunit/regress/regress-grow-store-smi-check.js
+++ b/test/mjsunit/d8-performance-now.js
@@ -27,27 +27,34 @@
 
 // Flags: --allow-natives-syntax
 
-// The below test function was generated from part of a WebKit layout
-// test library setup routine: fast/canvas/webgl/resources/pnglib.js
+// Test the window.performance.now() function of d8.  This test only makes
+// sense with d8.
 
-function test(crc32) {
-  for (var i = 0; i < 256; i++) {
-    var c = i;
-    for (var j = 0; j < 8; j++) {
-      if (c & 1) {
-        c = -306674912 ^ ((c >> 1) & 0x7fffffff);
-      } else {
-        c = (c >> 1) & 0x7fffffff;
-      }
+// Don't run this test in gc stress mode. Time differences may be long
+// due to garbage collections.
+%SetFlags("--gc-interval=-1");
+%SetFlags("--nostress-compaction");
+
+(function run() {
+  var start_test = window.performance.now();
+  // Let the retry run for maximum 100ms to reduce flakiness.
+  for (var start = window.performance.now();
+       start - start_test < 100;
+       start = window.performance.now()) {
+    var end = window.performance.now();
+    assertTrue(start >= start_test);
+    assertTrue(end >= start);
+    while (end - start == 0) {
+      var next = window.performance.now();
+      assertTrue(next >= end);
+      end = next;
+    }
+    if (end - start <= 1) {
+      // Found (sub-)millisecond granularity.
+      return;
+    } else {
+      print("Timer difference too big: " + (end - start) + "ms");
     }
-    crc32[i] = c;
   }
-}
-
-var a = [0.5];
-for (var i = 0; i < 256; ++i) a[i] = i;
-
-test([0.5]);
-test(a);
-%OptimizeFunctionOnNextCall(test);
-test(a);
+  assertTrue(false);
+})()