[ Merge from http://go/wvgerrit/72183 ]
Adds basic metrics for the usage table header. This adds the last rev of
cdm_session.cpp that was merged to the wv repo.
Bug: http://b/112919252
Test: Unit tests. Manual GPlay
Change-Id: I9494caf6fcdfb3d335ea10fe8b712585e95c79e5