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

chrome/browser/chromeos/extensions/screenlock_private_apitest.cc

Index: chrome/browser/chromeos/extensions/screenlock_private_apitest.cc
diff --git a/chrome/browser/extensions/api/bookmarks/bookmark_apitest.cc b/chrome/browser/chromeos/extensions/screenlock_private_apitest.cc
similarity index 63%
copy from chrome/browser/extensions/api/bookmarks/bookmark_apitest.cc
copy to chrome/browser/chromeos/extensions/screenlock_private_apitest.cc
index ebd68287c6cccdd8c1172c859db82d2d675c1cdd..48b57a45dbc08913eb2ab6569479c6bce1509ba6 100644
--- a/chrome/browser/extensions/api/bookmarks/bookmark_apitest.cc
+++ b/chrome/browser/chromeos/extensions/screenlock_private_apitest.cc
@@ -4,6 +4,6 @@
 
 #include "chrome/browser/extensions/extension_apitest.h"
 
-IN_PROC_BROWSER_TEST_F(ExtensionApiTest, Bookmarks) {
-  ASSERT_TRUE(RunExtensionTest("bookmarks")) << message_;
+IN_PROC_BROWSER_TEST_F(ExtensionApiTest, ScreenlockPrivateApiTest) {
+  ASSERT_TRUE(RunExtensionTest("screenlockPrivate")) << message_;
 }