Add gpu_perftests to perfbots.

gpu/perftests/run_all_tests.cc

 // Copyright (c) 2015 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/test/launcher/unit_test_launcher.h"
 #include "base/test/test_suite.h"
 
 int main(int argc, char** argv) {
   base::TestSuite test_suite(argc, argv);
 
+  // Always run the perf tests serially, to avoid distorting
+  // perf measurements with randomness resulting from running
+  // in parallel.
   const auto& run_test_suite =
       base::Bind(&base::TestSuite::Run, base::Unretained(&test_suite));
-  return base::LaunchUnitTests(argc, argv, run_test_suite);
+  return base::LaunchUnitTestsSerially(argc, argv, run_test_suite);
 }