InputWidget: Update DOM value before firing 'change' event

It seems sensible not to fire events while the object is in
inconsistent state.

It was previously done in this order before 8b32c7d2 was done to fix
the behavior when #cleanUpValue is not a no-op.

Change-Id: I5cc59b5c2682ece6b0df303c07b0c4dfa32d95ed
Merge "InputWidget: Update DOM value before firing 'change' event"