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 9896d746195b62037643c32e285cf1111970a3d6..a87439dc1a55726425651e821f06448a611cacdc 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.
 };