Standardize "net" category trace events

net/http/http_cache_transaction.cc

Index: net/http/http_cache_transaction.cc
diff --git a/net/http/http_cache_transaction.cc b/net/http/http_cache_transaction.cc
index b8f1eb06b2f9eae0f29072e47e64ecadb800d03e..68f3d1c67a409ea9d89ad75021a7f42ea0de9d2b 100644
--- a/net/http/http_cache_transaction.cc
+++ b/net/http/http_cache_transaction.cc
@@ -41,6 +41,7 @@
 #include "net/http/http_request_info.h"
 #include "net/http/http_util.h"
 #include "net/log/net_log_event_type.h"
+#include "net/log/trace_constants.h"
 #include "net/ssl/ssl_cert_request_info.h"
 #include "net/ssl/ssl_config_service.h"
 
@@ -1265,7 +1266,8 @@ int HttpCache::Transaction::DoCacheToggleUnusedSincePrefetch() {
 int HttpCache::Transaction::DoCacheToggleUnusedSincePrefetchComplete(
     int result) {
   TRACE_EVENT0(
-      "net", "HttpCacheTransaction::DoCacheToggleUnusedSincePrefetchComplete");
+      kNetTracingCategory,
+      "HttpCacheTransaction::DoCacheToggleUnusedSincePrefetchComplete");
   // Restore the original value for this transaction.
   response_.unused_since_prefetch = !response_.unused_since_prefetch;
   next_state_ = STATE_CACHE_DISPATCH_VALIDATION;