cashew: add cros-debug support

DCHECK macro in default clause of switch statement is compiled out when
cashew is compiled NDEBUG, causing a compilation error. Replace with a
CHECK macro.

Uncomment use of google::ShutdownGoogleLogging now that we have updated
glog to version 0.3.1 (see issue 8823).

BUG=chromium-os:8800
TEST=USE=-cros-debug emerge-<board> cashew

Change-Id: Ib60933ca908c2d383e6e241fcf77c2e32e8b92f9

Review URL: http://codereview.chromium.org/5696004