Use base::Thread instead of single-threaded SequencedWorkerPool in TestLauncher.

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 a51d97e31207acc6c5e85e74eaacc8400e94170d..0d2151fd54a8f248eb851d53a2933f291a84d44e 100644
--- a/base/test/launcher/test_launcher.cc
+++ b/base/test/launcher/test_launcher.cc
@@ -19,6 +19,7 @@
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/macros.h"
+#include "base/memory/ptr_util.h"
 #include "base/message_loop/message_loop.h"
 #include "base/process/kill.h"
 #include "base/process/launch.h"
@@ -37,6 +38,7 @@
 #include "base/test/sequenced_worker_pool_owner.h"
 #include "base/test/test_switches.h"
 #include "base/test/test_timeouts.h"
+#include "base/threading/thread.h"
 #include "base/threading/thread_checker.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/time/time.h"
@@ -573,7 +575,7 @@ void TestLauncher::LaunchChildGTestProcess(
   // JSON summary.
   bool redirect_stdio = (parallel_jobs_ > 1) || BotModeEnabled();
 
-  worker_pool_owner_->pool()->PostWorkerTask(
+  GetTaskRunner()->PostTask(
       FROM_HERE,
       Bind(&DoLaunchChildTestProcess, new_command_line, timeout, options,
            redirect_stdio, RetainedRef(ThreadTaskRunnerHandle::Get()),
@@ -801,10 +803,10 @@ bool TestLauncher::Init() {
     force_run_broken_tests_ = true;
 
   if (command_line->HasSwitch(switches::kTestLauncherJobs)) {
-    int jobs = -1;
-    if (!StringToInt(command_line->GetSwitchValueASCII(
+    size_t jobs = 0U;
+    if (!StringToSizeT(command_line->GetSwitchValueASCII(
                          switches::kTestLauncherJobs), &jobs) ||
-        jobs < 0) {
+        !jobs) {
       LOG(ERROR) << "Invalid value for " << switches::kTestLauncherJobs;
       return false;
     }
@@ -813,13 +815,18 @@ bool TestLauncher::Init() {
   } else if (command_line->HasSwitch(kGTestFilterFlag) && !BotModeEnabled()) {
     // Do not run jobs in parallel by default if we are running a subset of
     // the tests and if bot mode is off.
-    parallel_jobs_ = 1;
+    parallel_jobs_ = 1U;
   }
 
   fprintf(stdout, "Using %" PRIuS " parallel jobs.\n", parallel_jobs_);
   fflush(stdout);
-  worker_pool_owner_.reset(
-      new SequencedWorkerPoolOwner(parallel_jobs_, "test_launcher"));
+  if (parallel_jobs_ > 1U) {
+    worker_pool_owner_ = MakeUnique<SequencedWorkerPoolOwner>(
+        parallel_jobs_, "test_launcher");
+  } else {
+    worker_thread_ = MakeUnique<Thread>("test_launcher");
+    worker_thread_->Start();
+  }
 
   if (command_line->HasSwitch(switches::kTestLauncherFilterFile) &&
       command_line->HasSwitch(kGTestFilterFlag)) {
@@ -1113,6 +1120,17 @@ void TestLauncher::OnOutputTimeout() {
   watchdog_timer_.Reset();
 }
 
+scoped_refptr<TaskRunner> TestLauncher::GetTaskRunner() {
+  // One and only one of |worker_pool_owner_| or |worker_thread_| should be
+  // ready.
+  DCHECK_NE(!!worker_pool_owner_, !!worker_thread_);
+
+  if (worker_pool_owner_)
+    return worker_pool_owner_->pool();
+  DCHECK(worker_thread_->IsRunning());
+  return worker_thread_->task_runner();
+}
+
 std::string GetTestOutputSnippet(const TestResult& result,
                                  const std::string& full_output) {
   size_t run_pos = full_output.find(std::string("[ RUN      ] ") +