[NOT FOR REVIEW] Instrument net/ with trace events.

net/disk_cache/blockfile/in_flight_backend_io.cc

Index: net/disk_cache/blockfile/in_flight_backend_io.cc
diff --git a/net/disk_cache/blockfile/in_flight_backend_io.cc b/net/disk_cache/blockfile/in_flight_backend_io.cc
index 307f7d2a8d09a2f35030929d055a1465e482b283..35fc7a5927b316a5d7f18517df77ef228e1e1f57 100644
--- a/net/disk_cache/blockfile/in_flight_backend_io.cc
+++ b/net/disk_cache/blockfile/in_flight_backend_io.cc
@@ -11,6 +11,7 @@
 #include "base/compiler_specific.h"
 #include "base/logging.h"
 #include "base/single_thread_task_runner.h"
+#include "base/trace_event/trace_event.h"
 #include "net/base/net_errors.h"
 #include "net/disk_cache/blockfile/backend_impl.h"
 #include "net/disk_cache/blockfile/entry_impl.h"
@@ -234,6 +235,7 @@ base::TimeDelta BackendIO::ElapsedTime() const {
 
 // Runs on the background thread.
 void BackendIO::ExecuteBackendOperation() {
+  TRACE_EVENT0("net", "net::BackendIO::ExecuteBackendOperation");
   switch (operation_) {
     case OP_INIT:
       result_ = backend_->SyncInit();