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

content/browser/browser_main_loop.h

Index: content/browser/browser_main_loop.h
diff --git a/content/browser/browser_main_loop.h b/content/browser/browser_main_loop.h
index 4a87f872a6e88226b2c0122fa2e6d27e1a3df85e..19a7f6217e7e7bcf4ba4932d131449706538668f 100644
--- a/content/browser/browser_main_loop.h
+++ b/content/browser/browser_main_loop.h
@@ -23,9 +23,17 @@ class SystemMonitor;
 #if defined(OS_CHROMEOS)
 class MemoryPressureObserverChromeOS;
 #endif
-namespace debug {
+namespace trace_event {
 class TraceMemoryController;
 class TraceEventSystemStatsMonitor;
+}  // namespace trace_event
+
+// This is added temporarily. Once the renaming of namespace usages
+// accross all folders are done, this will be removed.
+// TODO(ssid): crrev.com/837303004
+namespace debug {
+using ::base::trace_event::TraceEventSystemStatsMonitor;
+using ::base::trace_event::TraceMemoryController;
 }  // namespace debug
 }  // namespace base