An example of using Drive API v2 in Apps Script. This will add "commenter" permission to a specified file. Note that not all types of documents support this permission type. To use this you need to create a project in API Console, enable Drive API in Services and get the API key.

DriveCommenter.gs

function fileAddCommenter() {
  authorize();
  var fileId = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"; // <-- id of the document
  var key = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"; // <-- developer key
  var requestBody = {
    role: "reader",
    type: "user",
    value: "someone@somewhere.com",
    additionalRoles: ["commenter"]
  };
  var notify = false; // <-- e-mail notification parameter
  var params = {method: "post",
                oAuthServiceName: "drive",
                oAuthUseToken: "always",
                contentType: "application/json",
                payload: Utilities.jsonStringify(requestBody)
               };
  var request = UrlFetchApp.fetch("https://www.googleapis.com/drive/v2/files/"+fileId+"/permissions?sendNotificationEmails="+String(notify)+"&key="+key, params);
  Logger.log(request.getContentText());
}
 
function authorize() {
  var oauthConfig = UrlFetchApp.addOAuthService("drive");
  var scope = "https://www.googleapis.com/auth/drive";
  oauthConfig.setConsumerKey("anonymous");
  oauthConfig.setConsumerSecret("anonymous");
  oauthConfig.setRequestTokenUrl("https://www.google.com/accounts/OAuthGetRequestToken?scope="+scope);
  oauthConfig.setAuthorizationUrl("https://accounts.google.com/OAuthAuthorizeToken");    
  oauthConfig.setAccessTokenUrl("https://www.google.com/accounts/OAuthGetAccessToken");  
}