Add a BeforeCloseEvent to the CellTree so that a CloseEvent can be cancelled

Originally reported on Google Code with ID 5756

Found in GWT Release (e.g. 1.5.3, 1.6 RC): GWT 2.1.0

Encountered on OS / Browser (e.g. WinXP, IE6-7, FF3): All

Detailed description (please be as specific as possible):
We need to have certain nodes in the cell tree be non-collapsible.
For example, the root node. This is so that a certain section of the
tree is always available and viewable to the user.

It would be beneficial if we could have a BeforeCloseEvent and be able to add a BeforeCloseHandler
to test the id of a node and ignore the CloseEvent.

Shortest code snippet which demonstrates issue (please indicate where
actual result differs from expected result):

Workaround if you have one: None

Links to relevant GWT Developer Forum posts:
http://groups.google.com/group/google-web-toolkit/browse_thread/thread/b6fa6241270e6334#

Reported by ramonjsantiago on 2010-12-13 20:30:23

gwtproject / gwt

Add a BeforeCloseEvent to the CellTree so that a CloseEvent can be cancelled #5755