Log the tag in native log stream.

BUG=
R=glaznev@webrtc.org

Review URL: https://codereview.webrtc.org/1356143003 .

Cr-Commit-Position: refs/heads/master@{#10006}
diff --git a/webrtc/base/logging.cc b/webrtc/base/logging.cc
index 7e308c2..07cc380 100644
--- a/webrtc/base/logging.cc
+++ b/webrtc/base/logging.cc
@@ -184,6 +184,7 @@
                        const std::string& tag)
     : LogMessage(file, line, sev, ERRCTX_NONE, 0 /* err */, NULL /* module */) {
   tag_ = tag;
+  print_stream_ << tag << ": ";
 }
 
 LogMessage::~LogMessage() {