Plugins can replace the existing implementation with the statement:
DynamicItem.bind(binder(), WebSession.class).to(...);
in a module designated as a "<Gerrit-HttpModule>" in the manifest.
Just the Cache implementation used for web sessions can be changed
by binding to a subclass of the now abstract CacheBasedWebSession
which supplies the Cache in the superclass constructor.
This is a step towards solving web session issues with multi-master.
Change-Id: I255661a62cfcbfe07646cb90005764061d618f3d
3e107f55d7