function loadAllExtensionsInNativeDirectory(directory, baseUrl) {
        return _loadAll(directory, {baseUrl: baseUrl}, "main", loadExtension);
    }
Loads the extension that lives at baseUrl into its own Require.js context

@param {!string} directory, an absolute native path that contains a directory of extensions.
                 each subdirectory is interpreted as an independent extension
@param {!string} baseUrl, URL path relative to index.html that maps to the same place as directory
@return {!$.Promise} A promise object that is resolved when all extensions complete loading.