Add main for Tint unittests

BUG=tint:123

Change-Id: I10915ff259d0f22c4074e9df59c90d0fbe21c68b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2313099
Auto-Submit: Ryan Harrison <rharrison@chromium.org>
Commit-Queue: Jonathan Backer <backer@chromium.org>
Reviewed-by: Jonathan Backer <backer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#790888}

gpu/tint_unittests_main.cc

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/bind.h"
+#include "base/command_line.h"
+#include "base/message_loop/message_pump_type.h"
+#include "base/task/single_thread_task_executor.h"
+#include "base/test/launcher/unit_test_launcher.h"
+#include "base/test/test_suite.h"
+#include "testing/gmock/include/gmock/gmock.h"
+
+namespace {
+
+int RunHelper(base::TestSuite* test_suite) {
+  base::SingleThreadTaskExecutor io_task_executor(base::MessagePumpType::IO);
+  return test_suite->Run();
+}
+
+}  // namespace
+
+int main(int argc, char** argv) {
+  base::CommandLine::Init(argc, argv);
+  testing::InitGoogleMock(&argc, argv);
+  base::TestSuite test_suite(argc, argv);
+  int rt = base::LaunchUnitTestsSerially(
+      argc, argv, base::BindOnce(&RunHelper, base::Unretained(&test_suite)));
+  return rt;
+}