Add a logging_no_op.cc when enable_tracing==0.

This should hopefully fix static initializer warnings when rolling webrtc
in Chromium.

TEST=logging_unittest succeeds with enable_tracing==1 and fails appropriately with enable_tracing==0.

Review URL: https://webrtc-codereview.appspot.com/939026

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@3159 4adac7df-926f-26a2-2b94-8c16560cd09d
6 files changed