In AsyncApplyUpdate, the Safe Browsing update thread holds a reference
to 'Classifier'. In some scenarios(See Bug 1591112), the update
thread may be the last one holding the reference; hence the update
thread releases the 'Classifier' when the task is ended.
Classifier has to be created and destroyed in the same thread
because of the constrain of LazyIdelThread, in the current
implementation, it should be released by the worker thread.
This patch transfers the ownership of the reference of 'Classifier 'from the
update thread to the worker thread before its task is finished to make
sure we release 'Classifier' in the right thread.
Differential Revision: https://phabricator.services.mozilla.com/D53156
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extra : moz-landing-system : lando
83eed8b61a