Expand usage of platform-apps flag and permission features.

chrome/common/extensions/extension_manifest_constants.cc

Index: chrome/common/extensions/extension_manifest_constants.cc
diff --git a/chrome/common/extensions/extension_manifest_constants.cc b/chrome/common/extensions/extension_manifest_constants.cc
index d1fa89eea4aea30401ed018fbafc2817f11bc03f..67bef539a216ed77336d8e3c8b175cbae8b6c8d3 100644
--- a/chrome/common/extensions/extension_manifest_constants.cc
+++ b/chrome/common/extensions/extension_manifest_constants.cc
@@ -455,6 +455,10 @@ const char kOneUISurfaceOnly[] =
     "Only one of 'browser_action', 'page_action', and 'app' can be specified.";
 const char kPermissionNotAllowed[] =
     "Access to permission '*' denied.";
+const char kPlatformAppFlagRequired[] =
+    "Loading platform_app extension type is turned off by default. "
+    "You can enable this type with the --enable-platform-apps "
+    "command-line flag.";
 const char kReservedMessageFound[] =
     "Reserved key * found in message catalog.";
 #if defined(OS_CHROMEOS)