Add basic tracing support to the gtest launcher

base/test/launcher/test_launcher.cc

Index: base/test/launcher/test_launcher.cc
diff --git a/base/test/launcher/test_launcher.cc b/base/test/launcher/test_launcher.cc
index cfd08fbc49ca6d89c121076eddc3c5d60b125550..c23dc8cb542a3bc4762eea7479d9ce38be3a7ae8 100644
--- a/base/test/launcher/test_launcher.cc
+++ b/base/test/launcher/test_launcher.cc
@@ -31,6 +31,7 @@
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/test/gtest_util.h"
+#include "base/test/launcher/test_launcher_tracer.h"
 #include "base/test/launcher/test_results_tracker.h"
 #include "base/test/sequenced_worker_pool_owner.h"
 #include "base/test/test_switches.h"
@@ -90,6 +91,9 @@ LazyInstance<std::map<ProcessHandle, CommandLine> > g_live_processes
     = LAZY_INSTANCE_INITIALIZER;
 LazyInstance<Lock> g_live_processes_lock = LAZY_INSTANCE_INITIALIZER;
 
+// Performance trace generator.
+LazyInstance<TestLauncherTracer> g_tracer = LAZY_INSTANCE_INITIALIZER;
+
 #if defined(OS_POSIX)
 // Self-pipe that makes it possible to do complex shutdown handling
 // outside of the signal handler.
@@ -253,6 +257,8 @@ int LaunchChildTestProcessWithOptions(
     TimeDelta timeout,
     const TestLauncher::GTestProcessLaunchedCallback& launched_callback,
     bool* was_timeout) {
+  TimeTicks start_time(TimeTicks::Now());
+
 #if defined(OS_POSIX)
   // Make sure an option we rely on is present - see LaunchChildGTestProcess.
   DCHECK(options.new_process_group);
@@ -344,6 +350,9 @@ int LaunchChildTestProcessWithOptions(
     g_live_processes.Get().erase(process.Handle());
   }
 
+  g_tracer.Get().RecordProcessExecution(start_time,
+                                        TimeTicks::Now() - start_time);
+
   return exit_code;
 }
 
@@ -1034,6 +1043,13 @@ void TestLauncher::MaybeSaveSummaryAsJSON() {
       LOG(ERROR) << "Failed to save test launcher output summary.";
     }
   }
+  if (command_line->HasSwitch(switches::kTestLauncherTrace)) {
+    FilePath trace_path(
+        command_line->GetSwitchValuePath(switches::kTestLauncherTrace));
+    if (!g_tracer.Get().Dump(trace_path)) {
+      LOG(ERROR) << "Failed to save test launcher trace.";
+    }
+  }
 }
 
 void TestLauncher::OnLaunchTestProcessFinished(