Reland of Move tracing namespace from base::debug to base::trace_event.

base/trace_event/trace_event_unittest.cc

Index: base/trace_event/trace_event_unittest.cc
diff --git a/base/trace_event/trace_event_unittest.cc b/base/trace_event/trace_event_unittest.cc
index 47b5ab619437258243c229834ec67734da6d0bba..a6bc0d4e7ced91adee3001aafab01a20ae0e7a0c 100644
--- a/base/trace_event/trace_event_unittest.cc
+++ b/base/trace_event/trace_event_unittest.cc
@@ -25,7 +25,7 @@
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace base {
-namespace debug {
+namespace trace_event {
 
 namespace {
 
@@ -3079,6 +3079,5 @@ TEST(TraceOptionsTest, TraceOptionsToString) {
   }
 }
 
-
-}  // namespace debug
+}  // namespace trace_event
 }  // namespace base