Add a warning for missing fileBrowserHandler permission.

extensions/common/manifest_constants.cc

Index: extensions/common/manifest_constants.cc
diff --git a/extensions/common/manifest_constants.cc b/extensions/common/manifest_constants.cc
index 1c51334cba975b42b1c3a280e75023ef7179c875..d4506bdaf76cc8db6d79f44d9204c839f63255c3 100644
--- a/extensions/common/manifest_constants.cc
+++ b/extensions/common/manifest_constants.cc
@@ -361,6 +361,9 @@ const char kInvalidFileAccessValue[] =
     "Invalid value for 'file_access[*]'.";
 const char kInvalidFileBrowserHandler[] =
     "Invalid value for 'file_browser_handlers'.";
+const char kInvalidFileBrowserHandlerMissingPermission[] =
+    "Declaring file browser handlers requires the fileBrowserHandler manifest "
+    "permission.";
 const char kInvalidFileFiltersList[] =
     "Invalid value for 'file_filters'.";
 const char kInvalidFileFilterValue[] =