FieldDropdown.validateOptions_ bug

[duzc2]

Problem statement

[rachel-fenichel]

Next steps:

• use tuple instead of options, to validate the correct object
• add a passing test for the case where tuple is an array and a failing test for the case when tuple is anything else

The current code is too permissive, which probably leads to later bugs.

@duzc2 feel free to make a pull request for this one.

[RoboErikG]

Underlying bug has been fixed but this could still use a field_dropdown_test.js file in the jsunit folder before we close out the bug.