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..c8acd09b01c0d241c07582027ca3e46a6fd45f3c 100644
--- a/net/http/http_cache_transaction.cc
+++ b/net/http/http_cache_transaction.cc
@@ -33,6 +33,7 @@
 #include "net/base/auth.h"
 #include "net/base/load_flags.h"
 #include "net/base/load_timing_info.h"
+#include "net/base/trace_constants.h"
 #include "net/base/upload_data_stream.h"
 #include "net/cert/cert_status_flags.h"
 #include "net/cert/x509_certificate.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;