As part of the plan to render extension errors in the
inspector instead of the view, append an element to
contain the error. More specifically, the element is
a div that contains a LabelWidget (in which the error
message is displayed) and a ButtonWidget (to expand
and collapse the error).
Initially the error element is hidden, but if Parsoid
returns an error, the element will be shown. If the
error is longer than 1 line, it is truncated but can
be expanded. On closing the inspector, any remaining
error is collapsed and hidden.
Depends on I6002d9870d2b to work
Bug: T113172
Change-Id: Ie84130d4ac0da9a738bf98ad0a3677d47566d585
