Disable base/logging.h stderr logs by default for webrtc/ tests.
base/logging.h dumped to stderr by default in debug mode, but webrtc
"trace" (via system_wrappers/../logging.h) has that feature disabled by
default. This makes the two consistent.
Bonus: log the filename:line in base/logging.h, which exists in the
TEST=neteq_impl.cc logs (which use base/logging.h) no longer appear in
debug mode, unless --logs=true is passed. Filenames appear correctly.