The chrome.screenlockPrivate API allows select apps to control the ChromeOS ScreenLocker.

chrome/test/data/extensions/api_test/screenlockPrivate/test.js

Index: chrome/test/data/extensions/api_test/screenlockPrivate/test.js
diff --git a/chrome/test/data/extensions/api_test/screenlockPrivate/test.js b/chrome/test/data/extensions/api_test/screenlockPrivate/test.js
new file mode 100644
index 0000000000000000000000000000000000000000..bc0eda8c901e18eb9009c59611ca7eb035485067
--- /dev/null
+++ b/chrome/test/data/extensions/api_test/screenlockPrivate/test.js
@@ -0,0 +1,87 @@
+// getLocked(). if true then fail.
+// setLocked(true)
+// wait for onChanged. if timeout then fail.
+// getLocked(). if false then fail.
+// setLocked(false)
+// wait for onChanged. if timeout then fail.
+// getLocked(). if true then fail.
+// succeed
+
+var stage = 0;
+
+function now() {
+  return (new Date()).getTime();
+}
+
+function watchdog(wrapped) {

[Matt Perry, 2013/11/13 01:01:14]

Cool addition, but the test fixture has a built in timeout. I would just rely on
that and remove this to simplify the test code.

[benjhayden, 2013/11/13 17:17:51]

Done.

+  return function() {
+    watchdog.clear();
+    var result = wrapped.apply(this, arguments);
+    watchdog.clear();
+    if (result) {
+      watchdog.timer = window.setTimeout(function() {
+        chrome.test.fail('timeout after ' + (now() - watchdog.started) +
+                         'ms at stage ' + stage);
+      }, watchdog.timeoutMs);
+      watchdog.started = now();
+      console.debug('watchdog started at ' + watchdog.started +
+                    ' at stage ' + stage);
+    }
+    return result;
+  }
+}
+watchdog.timer = null;
+watchdog.timeoutMs = 2000;
+watchdog.started = 0;
+watchdog.clear = function() {
+  if (!watchdog.timer) {
+    return;
+  }
+  console.debug('watchdog cleared after ' + (now() - watchdog.started) + 'ms');
+  window.clearTimeout(watchdog.timer);
+  watchdog.timer = null;
+  watchdog.started = 0;
+};
+
+function gotLocked(locked) {
+  console.log('step stage=' + stage + ' locked=' + locked);

[Matt Perry, 2013/11/13 01:01:14]

remove the logs before checking in to reduce log spew

[benjhayden, 2013/11/13 17:17:51]

Done.

+  if (stage === 0) {
+    if (locked) {
+      chrome.test.fail('locked at stage ' + stage);
+    } else {
+      chrome.screenlockPrivate.setLocked(true);
+      ++stage;
+      return true;
+    }
+  } else if (stage === 1) {
+    if (!locked) {
+      chrome.test.fail('unlocked at stage ' + stage);
+    } else {
+      chrome.screenlockPrivate.setLocked(false);
+      ++stage;
+      return true;
+    }
+  } else if (stage === 2) {
+    if (locked) {
+      chrome.test.fail('locked at stage ' + stage);
+    } else {
+      chrome.test.succeed();
+    }
+  }
+}
+
+var step = watchdog(function() {
+  chrome.screenlockPrivate.getLocked(watchdog(gotLocked));
+});
+
+chrome.screenlockPrivate.onChanged.addListener(watchdog(function(locked) {
+  console.log('onChanged stage=' + stage + ' locked=' + locked);
+  if (locked != (1 == (stage % 2))) {
+    chrome.test.fail((locked ? '' : 'un') + 'locked at stage ' + stage +
+                     ' onChanged');
+  } else {
+    return step();
+  }
+}));
+
+step();