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

chrome/browser/extensions/extension_function_histogram_value.h

Index: chrome/browser/extensions/extension_function_histogram_value.h
diff --git a/chrome/browser/extensions/extension_function_histogram_value.h b/chrome/browser/extensions/extension_function_histogram_value.h
index 112c4ef7f90e2e01b2bb2ac6dbc17cf7b2508226..6dac45f500bbb81d387a7a7f7872f8cf1334607b 100644
--- a/chrome/browser/extensions/extension_function_histogram_value.h
+++ b/chrome/browser/extensions/extension_function_histogram_value.h
@@ -687,6 +687,9 @@ enum HistogramValue {
   BOOKMARKMANAGERPRIVATE_GETMETAINFO,
   BOOKMARKMANAGERPRIVATE_SETMETAINFO,
   FILESYSTEMPROVIDER_MOUNT,
+  SCREENLOCKPRIVATE_GETLOCKED,
+  SCREENLOCKPRIVATE_SETLOCKED,
+  SCREENLOCKPRIVATE_SHOWMESSAGE,
   ENUM_BOUNDARY // Last entry: Add new entries above.
 };