Expose "$262.agent.monotonicNow()" for use in testing Atomic operation timeouts. Bug: v8:7705

R=binji@chromium.org, franzih@chromium.org

Cq-Include-Trybots: luci.v8.try:v8_linux_noi18n_rel_ng
Change-Id: Ib6db8ec0b9980399e53e4b39f5c10150ca72f555
Reviewed-on: https://chromium-review.googlesource.com/1033426
Commit-Queue: Ben Smith <binji@chromium.org>
Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Reviewed-by: Ben Smith <binji@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52897}

AUTHORS

@@ -129,6 +129,7 @@ Qiuyi Zhang <qiuyi.zqy@alibaba-inc.com>
 Rafal Krypa <rafal@krypa.net>
 Refael Ackermann <refack@gmail.com>
 Rene Rebe <rene@exactcode.de>
+Rick Waldron <waldron.rick@gmail.com>
 Rob Wu <rob@robwu.nl>
 Robert Mustacchi <rm@fingolfin.org>
 Robert Nagy <robert.nagy@gmail.com>

test/test262/harness-agent.js

@@ -62,7 +62,11 @@ function workerScript(script) {
 
         sleep(s) { Atomics.wait(i32a, ${SLEEP_LOC}, 0, s); },
 
-        leaving() {}
+        leaving() {},
+
+        monotonicNow() {
+          return performance.now();
+        }
       }
     };`;
 }
@@ -103,7 +107,11 @@ var agent = {
     return pendingReports.shift() || null;
   },
 
-  sleep(s) { Atomics.wait(i32a, SLEEP_LOC, 0, s); }
+  sleep(s) { Atomics.wait(i32a, SLEEP_LOC, 0, s); },
+
+  monotonicNow() {
+    return performance.now();
+  }
 };
 return agent;