Log number of known dependencies if Dependency throws an exception

This can provide a modicum of insight into why Dependency may be failing
to retrieve the required class. If, for instance, there is a race
condition then we would expect to see a smaller number of known
dependencies.

Dependency.

Bug: 65560049
Test: request a non-registered depdency from Depdency.java, then read
the logs.

Change-Id: I583287d0b59da321ab590f53a86c2d9b357304b2