Add private system extension API to get system update status

chrome/test/data/extensions/api_test/system/test.html

Index: chrome/test/data/extensions/api_test/system/test.html
diff --git a/chrome/test/data/extensions/api_test/system/test.html b/chrome/test/data/extensions/api_test/system/test.html
deleted file mode 100644
index d96bb3ed11a60be7a7f4f9398c3822869612b6c2..0000000000000000000000000000000000000000
--- a/chrome/test/data/extensions/api_test/system/test.html
+++ /dev/null
@@ -1,19 +0,0 @@
-<script>
-// System API test
-// Run with browser_tests --gtest_filter=ExtensionApiTest.SystemApi
-
-function expect(expected, message) {
-  return chrome.test.callbackPass(function(value) {
-    chrome.test.assertEq(expected, value, message);
-  });
-}
-
-chrome.test.runTests([
-  function getIncognitoModeAvailabilityTest() {
-    chrome.systemPrivate.getIncognitoModeAvailability(expect(
-        'disabled',
-        "Pref `chrome.system.getIncognitoModeAvailability` is expected to " +
-        "return 'disabled'"));
-  },
-]);
-</script>