[REVIEW REQUEST] Add text property to ComboBox

[Jonathan Giles]

>
> You're missing the point.
>>
>> I am saying that ComboBox API (or doc, for this matter), as of now, 
>> does not imply that the value is entered through a single text control.
>
> Correct, but there is a very big change that a combobox does have a 
> text based input, not 100% as you say, but chances are that it is 99%.
>

For a ComboBox instance, the chance of it having a TextField for input 
is 100%. Subclasses of ComboBoxBase can offer alternative input methods, 
and for this reason I do not want the text property to be on 
ComboBoxBase, but instead ComboBox.

-- Jonathan