DateTextBox does not always show an error with required=true

[Douglas Hays]

Run test_DateTextBox.html
Click on the 2nd textbox and the calendar popup appears. Select a date.
Erase all text in the same textbox w/o loosing focus.
Tab or click away and there's no error even though the field is required and the onChange should probably show undefined or blank.

[haysmark]

Seems that validation only happens while the calendar is open.

[haysmark]

Furthermore, this bug only happens the first time. If you repeat the procedure after you get the error state, it works as expected.

[haysmark]

This is an order of operations bug in ValidationTextBox?. The ValidationTextBox? template invokes _onMouse onblur, before focus manager calls Widget's _onBlur. But the error handling in validate(), which is triggered by _onMouse, checks to see if _onBlur has been called yet:

this.state = (isValid || (!this._hasBeenBlurred && isEmpty)) ? "" : "Error";

Hence, when you delete all of the text from a ValidationTextBox? for the first time, it doesn't matter whether a blank value is valid or invalid because we have allowed blank values to be valid the first time through. The code expects _onBlur to fire first, but this is not the case.

[haysmark]

Fixes #5971. Focus manager sets _hasBeenBlurred to true on widgets it blurs.

[Douglas Hays]

(In [12695]) Fixes #5971 !strict. Proxy commit for haysmark. Focus manager sets _hasBeenBlurred to true on widgets it blurs.