Remove cwd logic from generate_perf_json.py

tools/perf/generate_perf_json.py

 #!/usr/bin/env python
 # Copyright 2016 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.
 
 """Script to generate chromium.perf.json and chromium.perf.fyi.json in
 the src/testing/buildbot directory. Maintaining these files by hand is
 too unwieldy.
 """
 
@@ skipping 543 matching lines @@
 # Certain swarming bots are not sharding correctly with the new device affinity
 # algorithm.  Reverting to legacy algorithm to try and get them to complete.
 # See crbug.com/670284
 LEGACY_DEVICE_AFFIINITY_ALGORITHM = [
   'Win Zenbook Perf',
   'Win 10 High-DPI Perf',
   'Mac HDD Perf',
 ]
 
 def current_benchmarks(use_whitelist):
-  benchmarks_dir = os.path.join(os.getcwd(), 'benchmarks')
+  benchmarks_dir = os.path.join(src_dir(), 'tools', 'perf', 'benchmarks')
   top_level_dir = os.path.dirname(benchmarks_dir)
 
   all_benchmarks = discover.DiscoverClasses(
       benchmarks_dir, top_level_dir, benchmark_module.Benchmark,
       index_by_class_name=True).values()
   # Remove all blacklisted benchmarks
   for blacklisted in BENCHMARK_NAME_BLACKLIST:
     for benchmark in all_benchmarks:
       if benchmark.Name() == blacklisted:
         all_benchmarks.remove(benchmark)
         break
 
   if use_whitelist:
     all_benchmarks = (
         bench for bench in all_benchmarks
         if bench.Name() in BENCHMARK_NAME_WHITELIST)
   return sorted(all_benchmarks, key=lambda b: b.Name())
 
 
 # Returns a sorted list of (benchmark, avg_runtime) pairs for every
 # benchmark in the all_benchmarks list where avg_runtime is in seconds.  Also
 # returns a list of benchmarks whose run time have not been seen before
 def get_sorted_benchmark_list_by_time(all_benchmarks):
   runtime_list = []
   benchmark_avgs = {}
   new_benchmarks = []
+  timing_file_path = os.path.join(src_dir(), 'tools', 'perf',
+      'desktop_benchmark_avg_times.json')
   # Load in the avg times as calculated on Nov 1st, 2016
-  with open('desktop_benchmark_avg_times.json') as f:
+  with open(timing_file_path) as f:
     benchmark_avgs = json.load(f)
 
   for benchmark in all_benchmarks:
     benchmark_avg_time = benchmark_avgs.get(benchmark.Name(), None)
     if benchmark_avg_time is None:
       # Assume that this is a new benchmark that was added after 11/1/16 when
       # we generated the benchmarks. Use the old affinity algorithm after
       # we have given the rest the same distribution, add it to the
       # new benchmarks list.
       new_benchmarks.append(benchmark)
@@ skipping 73 matching lines @@
         scripts = generate_script_tests(waterfall['name'], name, shard + 1)
         if scripts:
           tests[tester_name] = {
             'scripts': sorted(scripts, key=lambda x: x['name'])
           }
 
   tests['AAAAA1 AUTOGENERATED FILE DO NOT EDIT'] = {}
   tests['AAAAA2 See //tools/perf/generate_perf_json.py to make changes'] = {}
   filename = '%s.json' % waterfall['name']
 
-  src_dir = os.path.dirname(os.path.dirname(os.getcwd()))
-
-  with open(os.path.join(src_dir, 'testing', 'buildbot', filename), 'w') as fp:
+  buildbot_dir = os.path.join(src_dir(), 'testing', 'buildbot')
+  with open(os.path.join(buildbot_dir, filename), 'w') as fp:
     json.dump(tests, fp, indent=2, separators=(',', ': '), sort_keys=True)
     fp.write('\n')
 
-def chdir_to_parent_directory():
-  parent_directory = os.path.dirname(os.path.abspath(__file__))
-  os.chdir(parent_directory)
+def src_dir():
+  file_path = os.path.abspath(__file__)
+  return os.path.dirname(os.path.dirname(os.path.dirname(file_path)))
 
 def main():
-  chdir_to_parent_directory()
-
   waterfall = get_waterfall_config()
   waterfall['name'] = 'chromium.perf'
   fyi_waterfall = get_fyi_waterfall_config()
   fyi_waterfall['name'] = 'chromium.perf.fyi'
 
   generate_all_tests(fyi_waterfall)
   generate_all_tests(waterfall)
   return 0
 
 if __name__ == '__main__':
   sys.exit(main())