Add back the WEBRTC_DIRECT_TRACE flag.

BUG=
R=andresp@webrtc.org, andrew@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/1596004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@4201 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/webrtc/system_wrappers/source/trace_impl.cc b/webrtc/system_wrappers/source/trace_impl.cc
index 4272b40..83c7377 100644
--- a/webrtc/system_wrappers/source/trace_impl.cc
+++ b/webrtc/system_wrappers/source/trace_impl.cc
@@ -414,6 +414,14 @@
     const char trace_message[WEBRTC_TRACE_MAX_MESSAGE_SIZE],
     const uint16_t length,
     const TraceLevel level) {
+// NOTE(andresp): Enabled externally.
+#ifdef WEBRTC_DIRECT_TRACE
+  if (callback_) {
+    callback_->Print(level, trace_message, length);
+  }
+  return;
+#endif
+
   CriticalSectionScoped lock(critsect_array_);
 
   if (next_free_idx_[active_queue_] >= WEBRTC_TRACE_MAX_QUEUE) {