code: function submitRequest( params ) {
  	debug( 'sending API request to proxy <iframe> %o', params );
  
  	// `formData` needs to be patched if it contains `File` objects to work around
  	// a Chrome bug. See `patchFileObjects` description for more details.
  	if ( params.formData ) {
  		patchFileObjects( params.formData );
  	}
  
  	iframe.contentWindow.postMessage( postStrings ? JSON.stringify( params ) : params, proxyOrigin );
  }
docs: Calls the `postMessage()` function on the <iframe>.
  
  @param {Object} params
  @api private