Print the filename of the trace data for the perf test

It is not clear which file stores the tracing data when --trace-dir
is specified.

Bug: none
Test: manually
Change-Id: I6e80e8f62adfa2091d271eaef1732891b69e33ca
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1769801Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Jun Mukai <mukai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#690410}

chrome/test/base/perf/performance_test.cc

@@ -129,6 +129,7 @@ void PerformanceTest::TearDownOnMainThread() {
         base::CommandLine::ForCurrentProcess()->GetSwitchValuePath(kTraceDir);
     base::FilePath trace_file;
     CHECK(base::CreateTemporaryFileInDir(dir, &trace_file));
+    LOG(INFO) << "Created the trace file: " << trace_file;
 
     auto trace_data_endpoint = content::TracingController::CreateFileEndpoint(
         trace_file, runloop.QuitClosure());