It's pretty common for different parts of a WebAPIResource subclass to

perform a get_object() call either on itself or on another resource.

This will happen in get_queryset() and in the permission-checking

functions. These checks are time-consuming and result in excess

database queries.
The built-in get_object() now supports caching of these objects. The

caches are tied to the request, so any redundant get_object() calls

taking place within that request will just use the original call's

result.

Djblets and Review Board unit tests pass.
Review Board unit tests gained nearly a 2 second increase in speed for

the API tests.
Tested a few resources I suspected had redundant calls. Saw the query counts

drop.