Re-establish ASSERTS that were dropped in  crrev.com/180363004. Add RELEASE_ASSERT to Dispose method,  which shouldn't be called with an empty value.
Re-establish ASSERTS that were dropped in  crrev.com/180363004. Add RELEASE_ASSERT to Dispose method, 
which shouldn't be called with an empty value.

(This shouldn't happen; but it would explain the stack trace in
the referenced issue.)

R=jochen@chromium.org
BUG=368095

Review URL: https://codereview.chromium.org/268143002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@173336 bbb929c8-8fbe-4397-9dbb-9b2b20218538

primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs