Implement chrome.systemPrivate.getIncognitoModeAvailability extension API function

chrome/browser/extensions/extension_preference_api_constants.cc

Index: chrome/browser/extensions/extension_preference_api_constants.cc
diff --git a/chrome/browser/extensions/extension_preference_api_constants.cc b/chrome/browser/extensions/extension_preference_api_constants.cc
index 9f4d3331ed3a384177a68f0d7eea94d539e7fb9d..3157fcfe26204cbcc03cd320ad69ed7aee26c04c 100644
--- a/chrome/browser/extensions/extension_preference_api_constants.cc
+++ b/chrome/browser/extensions/extension_preference_api_constants.cc
@@ -21,5 +21,11 @@ const char kPermissionErrorMessage[] =
     "You do not have permission to access the preference '*'. "
     "Be sure to declare in your manifest what permissions you need.";
 
+const char kCannotModifyReadOnlyMessage[] =
+    "You cannot modify the read-only preference '*'.";
+
+const char kInvalidParameter[] =
+    "You passed an invalid parameter.";
+
 }  // extension_preference_api_constants