[mb] Copy MB from Chromium repo

tools/mb/mb.py

+#!/usr/bin/env python
+# Copyright 2016 the V8 project authors. All rights reserved.
+# Copyright 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.
+
+"""MB - the Meta-Build wrapper around GYP and GN
+
+MB is a wrapper script for GYP and GN that can be used to generate build files
+for sets of canned configurations and analyze them.
+"""
+
+from __future__ import print_function
+
+import argparse
+import ast
+import errno
+import json
+import os
+import pipes
+import pprint
+import re
+import shutil
+import sys
+import subprocess
+import tempfile
+import traceback
+import urllib2
+
+from collections import OrderedDict
+
+CHROMIUM_SRC_DIR = os.path.dirname(os.path.dirname(os.path.dirname(
+    os.path.abspath(__file__))))
+sys.path = [os.path.join(CHROMIUM_SRC_DIR, 'build')] + sys.path
+
+import gn_helpers
+
+
+def main(args):
+  mbw = MetaBuildWrapper()
+  return mbw.Main(args)
+
+
+class MetaBuildWrapper(object):
+  def __init__(self):
+    self.chromium_src_dir = CHROMIUM_SRC_DIR
+    self.default_config = os.path.join(self.chromium_src_dir, 'infra', 'mb',
+                                       'mb_config.pyl')
+    self.executable = sys.executable
+    self.platform = sys.platform
+    self.sep = os.sep
+    self.args = argparse.Namespace()
+    self.configs = {}
+    self.masters = {}
+    self.mixins = {}
+
+  def Main(self, args):
+    self.ParseArgs(args)
+    try:
+      ret = self.args.func()
+      if ret:
+        self.DumpInputFiles()
+      return ret
+    except KeyboardInterrupt:
+      self.Print('interrupted, exiting', stream=sys.stderr)
+      return 130
+    except Exception:
+      self.DumpInputFiles()
+      s = traceback.format_exc()
+      for l in s.splitlines():
+        self.Print(l)
+      return 1
+
+  def ParseArgs(self, argv):
+    def AddCommonOptions(subp):
+      subp.add_argument('-b', '--builder',
+                        help='builder name to look up config from')
+      subp.add_argument('-m', '--master',
+                        help='master name to look up config from')
+      subp.add_argument('-c', '--config',
+                        help='configuration to analyze')
+      subp.add_argument('--phase', type=int,
+                        help=('build phase for a given build '
+                              '(int in [1, 2, ...))'))
+      subp.add_argument('-f', '--config-file', metavar='PATH',
+                        default=self.default_config,
+                        help='path to config file '
+                            '(default is //tools/mb/mb_config.pyl)')
+      subp.add_argument('-g', '--goma-dir',
+                        help='path to goma directory')
+      subp.add_argument('--gyp-script', metavar='PATH',
+                        default=self.PathJoin('build', 'gyp_chromium'),
+                        help='path to gyp script relative to project root '
+                             '(default is %(default)s)')
+      subp.add_argument('--android-version-code',
+                        help='Sets GN arg android_default_version_code and '
+                             'GYP_DEFINE app_manifest_version_code')
+      subp.add_argument('--android-version-name',
+                        help='Sets GN arg android_default_version_name and '
+                             'GYP_DEFINE app_manifest_version_name')
+      subp.add_argument('-n', '--dryrun', action='store_true',
+                        help='Do a dry run (i.e., do nothing, just print '
+                             'the commands that will run)')
+      subp.add_argument('-v', '--verbose', action='store_true',
+                        help='verbose logging')
+
+    parser = argparse.ArgumentParser(prog='mb')
+    subps = parser.add_subparsers()
+
+    subp = subps.add_parser('analyze',
+                            help='analyze whether changes to a set of files '
+                                 'will cause a set of binaries to be rebuilt.')
+    AddCommonOptions(subp)
+    subp.add_argument('path', nargs=1,
+                      help='path build was generated into.')
+    subp.add_argument('input_path', nargs=1,
+                      help='path to a file containing the input arguments '
+                           'as a JSON object.')
+    subp.add_argument('output_path', nargs=1,
+                      help='path to a file containing the output arguments '
+                           'as a JSON object.')
+    subp.set_defaults(func=self.CmdAnalyze)
+
+    subp = subps.add_parser('gen',
+                            help='generate a new set of build files')
+    AddCommonOptions(subp)
+    subp.add_argument('--swarming-targets-file',
+                      help='save runtime dependencies for targets listed '
+                           'in file.')
+    subp.add_argument('path', nargs=1,
+                      help='path to generate build into')
+    subp.set_defaults(func=self.CmdGen)
+
+    subp = subps.add_parser('isolate',
+                            help='generate the .isolate files for a given'
+                                 'binary')
+    AddCommonOptions(subp)
+    subp.add_argument('path', nargs=1,
+                      help='path build was generated into')
+    subp.add_argument('target', nargs=1,
+                      help='ninja target to generate the isolate for')
+    subp.set_defaults(func=self.CmdIsolate)
+
+    subp = subps.add_parser('lookup',
+                            help='look up the command for a given config or '
+                                 'builder')
+    AddCommonOptions(subp)
+    subp.set_defaults(func=self.CmdLookup)
+
+    subp = subps.add_parser(
+        'run',
+        help='build and run the isolated version of a '
+             'binary',
+        formatter_class=argparse.RawDescriptionHelpFormatter)
+    subp.description = (
+        'Build, isolate, and run the given binary with the command line\n'
+        'listed in the isolate. You may pass extra arguments after the\n'
+        'target; use "--" if the extra arguments need to include switches.\n'
+        '\n'
+        'Examples:\n'
+        '\n'
+        '  % tools/mb/mb.py run -m chromium.linux -b "Linux Builder" \\\n'
+        '    //out/Default content_browsertests\n'
+        '\n'
+        '  % tools/mb/mb.py run out/Default content_browsertests\n'
+        '\n'
+        '  % tools/mb/mb.py run out/Default content_browsertests -- \\\n'
+        '    --test-launcher-retry-limit=0'
+        '\n'
+    )
+
+    AddCommonOptions(subp)
+    subp.add_argument('-j', '--jobs', dest='jobs', type=int,
+                      help='Number of jobs to pass to ninja')
+    subp.add_argument('--no-build', dest='build', default=True,
+                      action='store_false',
+                      help='Do not build, just isolate and run')
+    subp.add_argument('path', nargs=1,
+                      help=('path to generate build into (or use).'
+                            ' This can be either a regular path or a '
+                            'GN-style source-relative path like '
+                            '//out/Default.'))
+    subp.add_argument('target', nargs=1,
+                      help='ninja target to build and run')
+    subp.add_argument('extra_args', nargs='*',
+                      help=('extra args to pass to the isolate to run. Use '
+                            '"--" as the first arg if you need to pass '
+                            'switches'))
+    subp.set_defaults(func=self.CmdRun)
+
+    subp = subps.add_parser('validate',
+                            help='validate the config file')
+    subp.add_argument('-f', '--config-file', metavar='PATH',
+                      default=self.default_config,
+                      help='path to config file '
+                          '(default is //infra/mb/mb_config.pyl)')
+    subp.set_defaults(func=self.CmdValidate)
+
+    subp = subps.add_parser('audit',
+                            help='Audit the config file to track progress')
+    subp.add_argument('-f', '--config-file', metavar='PATH',
+                      default=self.default_config,
+                      help='path to config file '
+                          '(default is //infra/mb/mb_config.pyl)')
+    subp.add_argument('-i', '--internal', action='store_true',
+                      help='check internal masters also')
+    subp.add_argument('-m', '--master', action='append',
+                      help='master to audit (default is all non-internal '
+                           'masters in file)')
+    subp.add_argument('-u', '--url-template', action='store',
+                      default='https://build.chromium.org/p/'
+                              '{master}/json/builders',
+                      help='URL scheme for JSON APIs to buildbot '
+                           '(default: %(default)s) ')
+    subp.add_argument('-c', '--check-compile', action='store_true',
+                      help='check whether tbd and master-only bots actually'
+                           ' do compiles')
+    subp.set_defaults(func=self.CmdAudit)
+
+    subp = subps.add_parser('help',
+                            help='Get help on a subcommand.')
+    subp.add_argument(nargs='?', action='store', dest='subcommand',
+                      help='The command to get help for.')
+    subp.set_defaults(func=self.CmdHelp)
+
+    self.args = parser.parse_args(argv)
+
+  def DumpInputFiles(self):
+
+    def DumpContentsOfFilePassedTo(arg_name, path):
+      if path and self.Exists(path):
+        self.Print("\n# To recreate the file passed to %s:" % arg_name)
+        self.Print("%% cat > %s <<EOF)" % path)
+        contents = self.ReadFile(path)
+        self.Print(contents)
+        self.Print("EOF\n%\n")
+
+    if getattr(self.args, 'input_path', None):
+      DumpContentsOfFilePassedTo(
+          'argv[0] (input_path)', self.args.input_path[0])
+    if getattr(self.args, 'swarming_targets_file', None):
+      DumpContentsOfFilePassedTo(
+          '--swarming-targets-file', self.args.swarming_targets_file)
+
+  def CmdAnalyze(self):
+    vals = self.Lookup()
+    self.ClobberIfNeeded(vals)
+    if vals['type'] == 'gn':
+      return self.RunGNAnalyze(vals)
+    else:
+      return self.RunGYPAnalyze(vals)
+
+  def CmdGen(self):
+    vals = self.Lookup()
+    self.ClobberIfNeeded(vals)
+    if vals['type'] == 'gn':
+      return self.RunGNGen(vals)
+    else:
+      return self.RunGYPGen(vals)
+
+  def CmdHelp(self):
+    if self.args.subcommand:
+      self.ParseArgs([self.args.subcommand, '--help'])
+    else:
+      self.ParseArgs(['--help'])
+
+  def CmdIsolate(self):
+    vals = self.GetConfig()
+    if not vals:
+      return 1
+
+    if vals['type'] == 'gn':
+      return self.RunGNIsolate(vals)
+    else:
+      return self.Build('%s_run' % self.args.target[0])
+
+  def CmdLookup(self):
+    vals = self.Lookup()
+    if vals['type'] == 'gn':
+      cmd = self.GNCmd('gen', '_path_')
+      gn_args = self.GNArgs(vals)
+      self.Print('\nWriting """\\\n%s""" to _path_/args.gn.\n' % gn_args)
+      env = None
+    else:
+      cmd, env = self.GYPCmd('_path_', vals)
+
+    self.PrintCmd(cmd, env)
+    return 0
+
+  def CmdRun(self):
+    vals = self.GetConfig()
+    if not vals:
+      return 1
+
+    build_dir = self.args.path[0]
+    target = self.args.target[0]
+
+    if vals['type'] == 'gn':
+      if self.args.build:
+        ret = self.Build(target)
+        if ret:
+          return ret
+      ret = self.RunGNIsolate(vals)
+      if ret:
+        return ret
+    else:
+      ret = self.Build('%s_run' % target)
+      if ret:
+        return ret
+
+    cmd = [
+        self.executable,
+        self.PathJoin('tools', 'swarming_client', 'isolate.py'),
+        'run',
+        '-s',
+        self.ToSrcRelPath('%s/%s.isolated' % (build_dir, target)),
+    ]
+    if self.args.extra_args:
+        cmd += ['--'] + self.args.extra_args
+
+    ret, _, _ = self.Run(cmd, force_verbose=False, buffer_output=False)
+
+    return ret
+
+  def CmdValidate(self, print_ok=True):
+    errs = []
+
+    # Read the file to make sure it parses.
+    self.ReadConfigFile()
+
+    # Build a list of all of the configs referenced by builders.
+    all_configs = {}
+    for master in self.masters:
+      for config in self.masters[master].values():
+        if isinstance(config, list):
+          for c in config:
+            all_configs[c] = master
+        else:
+          all_configs[config] = master
+
+    # Check that every referenced args file or config actually exists.
+    for config, loc in all_configs.items():
+      if config.startswith('//'):
+        if not self.Exists(self.ToAbsPath(config)):
+          errs.append('Unknown args file "%s" referenced from "%s".' %
+                      (config, loc))
+      elif not config in self.configs:
+        errs.append('Unknown config "%s" referenced from "%s".' %
+                    (config, loc))
+
+    # Check that every actual config is actually referenced.
+    for config in self.configs:
+      if not config in all_configs:
+        errs.append('Unused config "%s".' % config)
+
+    # Figure out the whole list of mixins, and check that every mixin
+    # listed by a config or another mixin actually exists.
+    referenced_mixins = set()
+    for config, mixins in self.configs.items():
+      for mixin in mixins:
+        if not mixin in self.mixins:
+          errs.append('Unknown mixin "%s" referenced by config "%s".' %
+                      (mixin, config))
+        referenced_mixins.add(mixin)
+
+    for mixin in self.mixins:
+      for sub_mixin in self.mixins[mixin].get('mixins', []):
+        if not sub_mixin in self.mixins:
+          errs.append('Unknown mixin "%s" referenced by mixin "%s".' %
+                      (sub_mixin, mixin))
+        referenced_mixins.add(sub_mixin)
+
+    # Check that every mixin defined is actually referenced somewhere.
+    for mixin in self.mixins:
+      if not mixin in referenced_mixins:
+        errs.append('Unreferenced mixin "%s".' % mixin)
+
+    if errs:
+      raise MBErr(('mb config file %s has problems:' % self.args.config_file) +
+                    '\n  ' + '\n  '.join(errs))
+
+    if print_ok:
+      self.Print('mb config file %s looks ok.' % self.args.config_file)
+    return 0
+
+  def CmdAudit(self):
+    """Track the progress of the GYP->GN migration on the bots."""
+
+    # First, make sure the config file is okay, but don't print anything
+    # if it is (it will throw an error if it isn't).
+    self.CmdValidate(print_ok=False)
+
+    stats = OrderedDict()
+    STAT_MASTER_ONLY = 'Master only'
+    STAT_CONFIG_ONLY = 'Config only'
+    STAT_TBD = 'Still TBD'
+    STAT_GYP = 'Still GYP'
+    STAT_DONE = 'Done (on GN)'
+    stats[STAT_MASTER_ONLY] = 0
+    stats[STAT_CONFIG_ONLY] = 0
+    stats[STAT_TBD] = 0
+    stats[STAT_GYP] = 0
+    stats[STAT_DONE] = 0
+
+    def PrintBuilders(heading, builders, notes):
+      stats.setdefault(heading, 0)
+      stats[heading] += len(builders)
+      if builders:
+        self.Print('  %s:' % heading)
+        for builder in sorted(builders):
+          self.Print('    %s%s' % (builder, notes[builder]))
+
+    self.ReadConfigFile()
+
+    masters = self.args.master or self.masters
+    for master in sorted(masters):
+      url = self.args.url_template.replace('{master}', master)
+
+      self.Print('Auditing %s' % master)
+
+      MASTERS_TO_SKIP = (
+        'client.skia',
+        'client.v8.fyi',
+        'tryserver.v8',
+      )
+      if master in MASTERS_TO_SKIP:
+        # Skip these bots because converting them is the responsibility of
+        # those teams and out of scope for the Chromium migration to GN.
+        self.Print('  Skipped (out of scope)')
+        self.Print('')
+        continue
+
+      INTERNAL_MASTERS = ('official.desktop', 'official.desktop.continuous',
+                          'internal.client.kitchensync')
+      if master in INTERNAL_MASTERS and not self.args.internal:
+        # Skip these because the servers aren't accessible by default ...
+        self.Print('  Skipped (internal)')
+        self.Print('')
+        continue
+
+      try:
+        # Fetch the /builders contents from the buildbot master. The
+        # keys of the dict are the builder names themselves.
+        json_contents = self.Fetch(url)
+        d = json.loads(json_contents)
+      except Exception as e:
+        self.Print(str(e))
+        return 1
+
+      config_builders = set(self.masters[master])
+      master_builders = set(d.keys())
+      both = master_builders & config_builders
+      master_only = master_builders - config_builders
+      config_only = config_builders - master_builders
+      tbd = set()
+      gyp = set()
+      done = set()
+      notes = {builder: '' for builder in config_builders | master_builders}
+
+      for builder in both:
+        config = self.masters[master][builder]
+        if config == 'tbd':
+          tbd.add(builder)
+        elif isinstance(config, list):
+          vals = self.FlattenConfig(config[0])
+          if vals['type'] == 'gyp':
+            gyp.add(builder)
+          else:
+            done.add(builder)
+        elif config.startswith('//'):
+          done.add(builder)
+        else:
+          vals = self.FlattenConfig(config)
+          if vals['type'] == 'gyp':
+            gyp.add(builder)
+          else:
+            done.add(builder)
+
+      if self.args.check_compile and (tbd or master_only):
+        either = tbd | master_only
+        for builder in either:
+          notes[builder] = ' (' + self.CheckCompile(master, builder) +')'
+
+      if master_only or config_only or tbd or gyp:
+        PrintBuilders(STAT_MASTER_ONLY, master_only, notes)
+        PrintBuilders(STAT_CONFIG_ONLY, config_only, notes)
+        PrintBuilders(STAT_TBD, tbd, notes)
+        PrintBuilders(STAT_GYP, gyp, notes)
+      else:
+        self.Print('  All GN!')
+
+      stats[STAT_DONE] += len(done)
+
+      self.Print('')
+
+    fmt = '{:<27} {:>4}'
+    self.Print(fmt.format('Totals', str(sum(int(v) for v in stats.values()))))
+    self.Print(fmt.format('-' * 27, '----'))
+    for stat, count in stats.items():
+      self.Print(fmt.format(stat, str(count)))
+
+    return 0
+
+  def GetConfig(self):
+    build_dir = self.args.path[0]
+
+    vals = {}
+    if self.args.builder or self.args.master or self.args.config:
+      vals = self.Lookup()
+      if vals['type'] == 'gn':
+        # Re-run gn gen in order to ensure the config is consistent with the
+        # build dir.
+        self.RunGNGen(vals)
+      return vals
+
+    mb_type_path = self.PathJoin(self.ToAbsPath(build_dir), 'mb_type')
+    if not self.Exists(mb_type_path):
+      toolchain_path = self.PathJoin(self.ToAbsPath(build_dir),
+                                     'toolchain.ninja')
+      if not self.Exists(toolchain_path):
+        self.Print('Must either specify a path to an existing GN build dir '
+                   'or pass in a -m/-b pair or a -c flag to specify the '
+                   'configuration')
+        return {}
+      else:
+        mb_type = 'gn'
+    else:
+      mb_type = self.ReadFile(mb_type_path).strip()
+
+    if mb_type == 'gn':
+      vals = self.GNValsFromDir(build_dir)
+    else:
+      vals = {}
+    vals['type'] = mb_type
+
+    return vals
+
+  def GNValsFromDir(self, build_dir):
+    args_contents = ""
+    gn_args_path = self.PathJoin(self.ToAbsPath(build_dir), 'args.gn')
+    if self.Exists(gn_args_path):
+      args_contents = self.ReadFile(gn_args_path)
+    gn_args = []
+    for l in args_contents.splitlines():
+      fields = l.split(' ')
+      name = fields[0]
+      val = ' '.join(fields[2:])
+      gn_args.append('%s=%s' % (name, val))
+
+    return {
+      'gn_args': ' '.join(gn_args),
+      'type': 'gn',
+    }
+
+  def Lookup(self):
+    vals = self.ReadBotConfig()
+    if not vals:
+      self.ReadConfigFile()
+      config = self.ConfigFromArgs()
+      if config.startswith('//'):
+        if not self.Exists(self.ToAbsPath(config)):
+          raise MBErr('args file "%s" not found' % config)
+        vals = {
+          'args_file': config,
+          'cros_passthrough': False,
+          'gn_args': '',
+          'gyp_crosscompile': False,
+          'gyp_defines': '',
+          'type': 'gn',
+        }
+      else:
+        if not config in self.configs:
+          raise MBErr('Config "%s" not found in %s' %
+                      (config, self.args.config_file))
+        vals = self.FlattenConfig(config)
+
+    # Do some basic sanity checking on the config so that we
+    # don't have to do this in every caller.
+    assert 'type' in vals, 'No meta-build type specified in the config'
+    assert vals['type'] in ('gn', 'gyp'), (
+        'Unknown meta-build type "%s"' % vals['gn_args'])
+
+    return vals
+
+  def ReadBotConfig(self):
+    if not self.args.master or not self.args.builder:
+      return {}
+    path = self.PathJoin(self.chromium_src_dir, 'ios', 'build', 'bots',
+                         self.args.master, self.args.builder + '.json')
+    if not self.Exists(path):
+      return {}
+
+    contents = json.loads(self.ReadFile(path))
+    gyp_vals = contents.get('GYP_DEFINES', {})
+    if isinstance(gyp_vals, dict):
+      gyp_defines = ' '.join('%s=%s' % (k, v) for k, v in gyp_vals.items())
+    else:
+      gyp_defines = ' '.join(gyp_vals)
+    gn_args = ' '.join(contents.get('gn_args', []))
+
+    return {
+        'args_file': '',
+        'cros_passthrough': False,
+        'gn_args': gn_args,
+        'gyp_crosscompile': False,
+        'gyp_defines': gyp_defines,
+        'type': contents.get('mb_type', ''),
+    }
+
+  def ReadConfigFile(self):
+    if not self.Exists(self.args.config_file):
+      raise MBErr('config file not found at %s' % self.args.config_file)
+
+    try:
+      contents = ast.literal_eval(self.ReadFile(self.args.config_file))
+    except SyntaxError as e:
+      raise MBErr('Failed to parse config file "%s": %s' %
+                 (self.args.config_file, e))
+
+    self.configs = contents['configs']
+    self.masters = contents['masters']
+    self.mixins = contents['mixins']
+
+  def ConfigFromArgs(self):
+    if self.args.config:
+      if self.args.master or self.args.builder:
+        raise MBErr('Can not specific both -c/--config and -m/--master or '
+                    '-b/--builder')
+
+      return self.args.config
+
+    if not self.args.master or not self.args.builder:
+      raise MBErr('Must specify either -c/--config or '
+                  '(-m/--master and -b/--builder)')
+
+    if not self.args.master in self.masters:
+      raise MBErr('Master name "%s" not found in "%s"' %
+                  (self.args.master, self.args.config_file))
+
+    if not self.args.builder in self.masters[self.args.master]:
+      raise MBErr('Builder name "%s"  not found under masters[%s] in "%s"' %
+                  (self.args.builder, self.args.master, self.args.config_file))
+
+    config = self.masters[self.args.master][self.args.builder]
+    if isinstance(config, list):
+      if self.args.phase is None:
+        raise MBErr('Must specify a build --phase for %s on %s' %
+                    (self.args.builder, self.args.master))
+      phase = int(self.args.phase)
+      if phase < 1 or phase > len(config):
+        raise MBErr('Phase %d out of bounds for %s on %s' %
+                    (phase, self.args.builder, self.args.master))
+      return config[phase-1]
+
+    if self.args.phase is not None:
+      raise MBErr('Must not specify a build --phase for %s on %s' %
+                  (self.args.builder, self.args.master))
+    return config
+
+  def FlattenConfig(self, config):
+    mixins = self.configs[config]
+    vals = {
+      'args_file': '',
+      'cros_passthrough': False,
+      'gn_args': [],
+      'gyp_defines': '',
+      'gyp_crosscompile': False,
+      'type': None,
+    }
+
+    visited = []
+    self.FlattenMixins(mixins, vals, visited)
+    return vals
+
+  def FlattenMixins(self, mixins, vals, visited):
+    for m in mixins:
+      if m not in self.mixins:
+        raise MBErr('Unknown mixin "%s"' % m)
+
+      visited.append(m)
+
+      mixin_vals = self.mixins[m]
+
+      if 'cros_passthrough' in mixin_vals:
+        vals['cros_passthrough'] = mixin_vals['cros_passthrough']
+      if 'gn_args' in mixin_vals:
+        if vals['gn_args']:
+          vals['gn_args'] += ' ' + mixin_vals['gn_args']
+        else:
+          vals['gn_args'] = mixin_vals['gn_args']
+      if 'gyp_crosscompile' in mixin_vals:
+        vals['gyp_crosscompile'] = mixin_vals['gyp_crosscompile']
+      if 'gyp_defines' in mixin_vals:
+        if vals['gyp_defines']:
+          vals['gyp_defines'] += ' ' + mixin_vals['gyp_defines']
+        else:
+          vals['gyp_defines'] = mixin_vals['gyp_defines']
+      if 'type' in mixin_vals:
+        vals['type'] = mixin_vals['type']
+
+      if 'mixins' in mixin_vals:
+        self.FlattenMixins(mixin_vals['mixins'], vals, visited)
+    return vals
+
+  def ClobberIfNeeded(self, vals):
+    path = self.args.path[0]
+    build_dir = self.ToAbsPath(path)
+    mb_type_path = self.PathJoin(build_dir, 'mb_type')
+    needs_clobber = False
+    new_mb_type = vals['type']
+    if self.Exists(build_dir):
+      if self.Exists(mb_type_path):
+        old_mb_type = self.ReadFile(mb_type_path)
+        if old_mb_type != new_mb_type:
+          self.Print("Build type mismatch: was %s, will be %s, clobbering %s" %
+                     (old_mb_type, new_mb_type, path))
+          needs_clobber = True
+      else:
+        # There is no 'mb_type' file in the build directory, so this probably
+        # means that the prior build(s) were not done through mb, and we
+        # have no idea if this was a GYP build or a GN build. Clobber it
+        # to be safe.
+        self.Print("%s/mb_type missing, clobbering to be safe" % path)
+        needs_clobber = True
+
+    if self.args.dryrun:
+      return
+
+    if needs_clobber:
+      self.RemoveDirectory(build_dir)
+
+    self.MaybeMakeDirectory(build_dir)
+    self.WriteFile(mb_type_path, new_mb_type)
+
+  def RunGNGen(self, vals):
+    build_dir = self.args.path[0]
+
+    cmd = self.GNCmd('gen', build_dir, '--check')
+    gn_args = self.GNArgs(vals)
+
+    # Since GN hasn't run yet, the build directory may not even exist.
+    self.MaybeMakeDirectory(self.ToAbsPath(build_dir))
+
+    gn_args_path = self.ToAbsPath(build_dir, 'args.gn')
+    self.WriteFile(gn_args_path, gn_args, force_verbose=True)
+
+    swarming_targets = []
+    if getattr(self.args, 'swarming_targets_file', None):
+      # We need GN to generate the list of runtime dependencies for
+      # the compile targets listed (one per line) in the file so
+      # we can run them via swarming. We use ninja_to_gn.pyl to convert
+      # the compile targets to the matching GN labels.
+      path = self.args.swarming_targets_file
+      if not self.Exists(path):
+        self.WriteFailureAndRaise('"%s" does not exist' % path,
+                                  output_path=None)
+      contents = self.ReadFile(path)
+      swarming_targets = set(contents.splitlines())
+      gn_isolate_map = ast.literal_eval(self.ReadFile(self.PathJoin(
+          self.chromium_src_dir, 'testing', 'buildbot', 'gn_isolate_map.pyl')))
+      gn_labels = []
+      err = ''
+      for target in swarming_targets:
+        target_name = self.GNTargetName(target)
+        if not target_name in gn_isolate_map:
+          err += ('test target "%s" not found\n' % target_name)
+        elif gn_isolate_map[target_name]['type'] == 'unknown':
+          err += ('test target "%s" type is unknown\n' % target_name)
+        else:
+          gn_labels.append(gn_isolate_map[target_name]['label'])
+
+      if err:
+          raise MBErr('Error: Failed to match swarming targets to %s:\n%s' %
+                      ('//testing/buildbot/gn_isolate_map.pyl', err))
+
+      gn_runtime_deps_path = self.ToAbsPath(build_dir, 'runtime_deps')
+      self.WriteFile(gn_runtime_deps_path, '\n'.join(gn_labels) + '\n')
+      cmd.append('--runtime-deps-list-file=%s' % gn_runtime_deps_path)
+
+    ret, _, _ = self.Run(cmd)
+    if ret:
+        # If `gn gen` failed, we should exit early rather than trying to
+        # generate isolates. Run() will have already logged any error output.
+        self.Print('GN gen failed: %d' % ret)
+        return ret
+
+    android = 'target_os="android"' in vals['gn_args']
+    for target in swarming_targets:
+      if android:
+        # Android targets may be either android_apk or executable. The former
+        # will result in runtime_deps associated with the stamp file, while the
+        # latter will result in runtime_deps associated with the executable.
+        target_name = self.GNTargetName(target)
+        label = gn_isolate_map[target_name]['label']
+        runtime_deps_targets = [
+            target_name + '.runtime_deps',
+            'obj/%s.stamp.runtime_deps' % label.replace(':', '/')]
+      elif gn_isolate_map[target]['type'] == 'gpu_browser_test':
+        if self.platform == 'win32':
+          runtime_deps_targets = ['browser_tests.exe.runtime_deps']
+        else:
+          runtime_deps_targets = ['browser_tests.runtime_deps']
+      elif (gn_isolate_map[target]['type'] == 'script' or
+            gn_isolate_map[target].get('label_type') == 'group'):
+        # For script targets, the build target is usually a group,
+        # for which gn generates the runtime_deps next to the stamp file
+        # for the label, which lives under the obj/ directory.
+        label = gn_isolate_map[target]['label']
+        runtime_deps_targets = [
+            'obj/%s.stamp.runtime_deps' % label.replace(':', '/')]
+      elif self.platform == 'win32':
+        runtime_deps_targets = [target + '.exe.runtime_deps']
+      else:
+        runtime_deps_targets = [target + '.runtime_deps']
+
+      for r in runtime_deps_targets:
+        runtime_deps_path = self.ToAbsPath(build_dir, r)
+        if self.Exists(runtime_deps_path):
+          break
+      else:
+        raise MBErr('did not generate any of %s' %
+                    ', '.join(runtime_deps_targets))
+
+      command, extra_files = self.GetIsolateCommand(target, vals,
+                                                    gn_isolate_map)
+
+      runtime_deps = self.ReadFile(runtime_deps_path).splitlines()
+
+      self.WriteIsolateFiles(build_dir, command, target, runtime_deps,
+                             extra_files)
+
+    return 0
+
+  def RunGNIsolate(self, vals):
+    gn_isolate_map = ast.literal_eval(self.ReadFile(self.PathJoin(
+        self.chromium_src_dir, 'testing', 'buildbot', 'gn_isolate_map.pyl')))
+
+    build_dir = self.args.path[0]
+    target = self.args.target[0]
+    target_name = self.GNTargetName(target)
+    command, extra_files = self.GetIsolateCommand(target, vals, gn_isolate_map)
+
+    label = gn_isolate_map[target_name]['label']
+    cmd = self.GNCmd('desc', build_dir, label, 'runtime_deps')
+    ret, out, _ = self.Call(cmd)
+    if ret:
+      if out:
+        self.Print(out)
+      return ret
+
+    runtime_deps = out.splitlines()
+
+    self.WriteIsolateFiles(build_dir, command, target, runtime_deps,
+                           extra_files)
+
+    ret, _, _ = self.Run([
+        self.executable,
+        self.PathJoin('tools', 'swarming_client', 'isolate.py'),
+        'check',
+        '-i',
+        self.ToSrcRelPath('%s/%s.isolate' % (build_dir, target)),
+        '-s',
+        self.ToSrcRelPath('%s/%s.isolated' % (build_dir, target))],
+        buffer_output=False)
+
+    return ret
+
+  def WriteIsolateFiles(self, build_dir, command, target, runtime_deps,
+                        extra_files):
+    isolate_path = self.ToAbsPath(build_dir, target + '.isolate')
+    self.WriteFile(isolate_path,
+      pprint.pformat({
+        'variables': {
+          'command': command,
+          'files': sorted(runtime_deps + extra_files),
+        }
+      }) + '\n')
+
+    self.WriteJSON(
+      {
+        'args': [
+          '--isolated',
+          self.ToSrcRelPath('%s/%s.isolated' % (build_dir, target)),
+          '--isolate',
+          self.ToSrcRelPath('%s/%s.isolate' % (build_dir, target)),
+        ],
+        'dir': self.chromium_src_dir,
+        'version': 1,
+      },
+      isolate_path + 'd.gen.json',
+    )
+
+  def GNCmd(self, subcommand, path, *args):
+    if self.platform == 'linux2':
+      subdir, exe = 'linux64', 'gn'
+    elif self.platform == 'darwin':
+      subdir, exe = 'mac', 'gn'
+    else:
+      subdir, exe = 'win', 'gn.exe'
+
+    gn_path = self.PathJoin(self.chromium_src_dir, 'buildtools', subdir, exe)
+
+    return [gn_path, subcommand, path] + list(args)
+
+  def GNArgs(self, vals):
+    if vals['cros_passthrough']:
+      if not 'GN_ARGS' in os.environ:
+        raise MBErr('MB is expecting GN_ARGS to be in the environment')
+      gn_args = os.environ['GN_ARGS']
+      if not re.search('target_os.*=.*"chromeos"', gn_args):
+        raise MBErr('GN_ARGS is missing target_os = "chromeos": (GN_ARGS=%s)' %
+                    gn_args)
+    else:
+      gn_args = vals['gn_args']
+
+    if self.args.goma_dir:
+      gn_args += ' goma_dir="%s"' % self.args.goma_dir
+
+    android_version_code = self.args.android_version_code
+    if android_version_code:
+      gn_args += ' android_default_version_code="%s"' % android_version_code
+
+    android_version_name = self.args.android_version_name
+    if android_version_name:
+      gn_args += ' android_default_version_name="%s"' % android_version_name
+
+    # Canonicalize the arg string into a sorted, newline-separated list
+    # of key-value pairs, and de-dup the keys if need be so that only
+    # the last instance of each arg is listed.
+    gn_args = gn_helpers.ToGNString(gn_helpers.FromGNArgs(gn_args))
+
+    args_file = vals.get('args_file', None)
+    if args_file:
+      gn_args = ('import("%s")\n' % vals['args_file']) + gn_args
+    return gn_args
+
+  def RunGYPGen(self, vals):
+    path = self.args.path[0]
+
+    output_dir = self.ParseGYPConfigPath(path)
+    cmd, env = self.GYPCmd(output_dir, vals)
+    ret, _, _ = self.Run(cmd, env=env)
+    return ret
+
+  def RunGYPAnalyze(self, vals):
+    output_dir = self.ParseGYPConfigPath(self.args.path[0])
+    if self.args.verbose:
+      inp = self.ReadInputJSON(['files', 'test_targets',
+                                'additional_compile_targets'])
+      self.Print()
+      self.Print('analyze input:')
+      self.PrintJSON(inp)
+      self.Print()
+
+    cmd, env = self.GYPCmd(output_dir, vals)
+    cmd.extend(['-f', 'analyzer',
+                '-G', 'config_path=%s' % self.args.input_path[0],
+                '-G', 'analyzer_output_path=%s' % self.args.output_path[0]])
+    ret, _, _ = self.Run(cmd, env=env)
+    if not ret and self.args.verbose:
+      outp = json.loads(self.ReadFile(self.args.output_path[0]))
+      self.Print()
+      self.Print('analyze output:')
+      self.PrintJSON(outp)
+      self.Print()
+
+    return ret
+
+  def GetIsolateCommand(self, target, vals, gn_isolate_map):
+    android = 'target_os="android"' in vals['gn_args']
+
+    # This needs to mirror the settings in //build/config/ui.gni:
+    # use_x11 = is_linux && !use_ozone.
+    use_x11 = (self.platform == 'linux2' and
+               not android and
+               not 'use_ozone=true' in vals['gn_args'])
+
+    asan = 'is_asan=true' in vals['gn_args']
+    msan = 'is_msan=true' in vals['gn_args']
+    tsan = 'is_tsan=true' in vals['gn_args']
+
+    target_name = self.GNTargetName(target)
+    test_type = gn_isolate_map[target_name]['type']
+
+    executable = gn_isolate_map[target_name].get('executable', target_name)
+    executable_suffix = '.exe' if self.platform == 'win32' else ''
+
+    cmdline = []
+    extra_files = []
+
+    if android and test_type != "script":
+      logdog_command = [
+          '--logdog-bin-cmd', './../../bin/logdog_butler',
+          '--project', 'chromium',
+          '--service-account-json',
+          '/creds/service_accounts/service-account-luci-logdog-publisher.json',
+          '--prefix', 'android/swarming/logcats/${SWARMING_TASK_ID}',
+          '--source', '${ISOLATED_OUTDIR}/logcats',
+          '--name', 'unified_logcats',
+      ]
+      test_cmdline = [
+          self.PathJoin('bin', 'run_%s' % target_name),
+          '--logcat-output-file', '${ISOLATED_OUTDIR}/logcats',
+          '--target-devices-file', '${SWARMING_BOT_FILE}',
+          '-v'
+      ]
+      cmdline = (['./../../build/android/test_wrapper/logdog_wrapper.py']
+                 + logdog_command + test_cmdline)
+    elif use_x11 and test_type == 'windowed_test_launcher':
+      extra_files = [
+          'xdisplaycheck',
+          '../../testing/test_env.py',
+          '../../testing/xvfb.py',
+      ]
+      cmdline = [
+        '../../testing/xvfb.py',
+        '.',
+        './' + str(executable) + executable_suffix,
+        '--brave-new-test-launcher',
+        '--test-launcher-bot-mode',
+        '--asan=%d' % asan,
+        '--msan=%d' % msan,
+        '--tsan=%d' % tsan,
+      ]
+    elif test_type in ('windowed_test_launcher', 'console_test_launcher'):
+      extra_files = [
+          '../../testing/test_env.py'
+      ]
+      cmdline = [
+          '../../testing/test_env.py',
+          './' + str(executable) + executable_suffix,
+          '--brave-new-test-launcher',
+          '--test-launcher-bot-mode',
+          '--asan=%d' % asan,
+          '--msan=%d' % msan,
+          '--tsan=%d' % tsan,
+      ]
+    elif test_type == 'gpu_browser_test':
+      extra_files = [
+          '../../testing/test_env.py'
+      ]
+      gtest_filter = gn_isolate_map[target]['gtest_filter']
+      cmdline = [
+          '../../testing/test_env.py',
+          './browser_tests' + executable_suffix,
+          '--test-launcher-bot-mode',
+          '--enable-gpu',
+          '--test-launcher-jobs=1',
+          '--gtest_filter=%s' % gtest_filter,
+      ]
+    elif test_type == 'script':
+      extra_files = [
+          '../../testing/test_env.py'
+      ]
+      cmdline = [
+          '../../testing/test_env.py',
+          '../../' + self.ToSrcRelPath(gn_isolate_map[target]['script'])
+      ]
+    elif test_type in ('raw'):
+      extra_files = []
+      cmdline = [
+          './' + str(target) + executable_suffix,
+      ]
+
+    else:
+      self.WriteFailureAndRaise('No command line for %s found (test type %s).'
+                                % (target, test_type), output_path=None)
+
+    cmdline += gn_isolate_map[target_name].get('args', [])
+
+    return cmdline, extra_files
+
+  def ToAbsPath(self, build_path, *comps):
+    return self.PathJoin(self.chromium_src_dir,
+                         self.ToSrcRelPath(build_path),
+                         *comps)
+
+  def ToSrcRelPath(self, path):
+    """Returns a relative path from the top of the repo."""
+    if path.startswith('//'):
+      return path[2:].replace('/', self.sep)
+    return self.RelPath(path, self.chromium_src_dir)
+
+  def ParseGYPConfigPath(self, path):
+    rpath = self.ToSrcRelPath(path)
+    output_dir, _, _ = rpath.rpartition(self.sep)
+    return output_dir
+
+  def GYPCmd(self, output_dir, vals):
+    if vals['cros_passthrough']:
+      if not 'GYP_DEFINES' in os.environ:
+        raise MBErr('MB is expecting GYP_DEFINES to be in the environment')
+      gyp_defines = os.environ['GYP_DEFINES']
+      if not 'chromeos=1' in gyp_defines:
+        raise MBErr('GYP_DEFINES is missing chromeos=1: (GYP_DEFINES=%s)' %
+                    gyp_defines)
+    else:
+      gyp_defines = vals['gyp_defines']
+
+    goma_dir = self.args.goma_dir
+
+    # GYP uses shlex.split() to split the gyp defines into separate arguments,
+    # so we can support backslashes and and spaces in arguments by quoting
+    # them, even on Windows, where this normally wouldn't work.
+    if goma_dir and ('\\' in goma_dir or ' ' in goma_dir):
+      goma_dir = "'%s'" % goma_dir
+
+    if goma_dir:
+      gyp_defines += ' gomadir=%s' % goma_dir
+
+    android_version_code = self.args.android_version_code
+    if android_version_code:
+      gyp_defines += ' app_manifest_version_code=%s' % android_version_code
+
+    android_version_name = self.args.android_version_name
+    if android_version_name:
+      gyp_defines += ' app_manifest_version_name=%s' % android_version_name
+
+    cmd = [
+        self.executable,
+        self.args.gyp_script,
+        '-G',
+        'output_dir=' + output_dir,
+    ]
+
+    # Ensure that we have an environment that only contains
+    # the exact values of the GYP variables we need.
+    env = os.environ.copy()
+
+    # This is a terrible hack to work around the fact that
+    # //tools/clang/scripts/update.py is invoked by GYP and GN but
+    # currently relies on an environment variable to figure out
+    # what revision to embed in the command line #defines.
+    # For GN, we've made this work via a gn arg that will cause update.py
+    # to get an additional command line arg, but getting that to work
+    # via GYP_DEFINES has proven difficult, so we rewrite the GYP_DEFINES
+    # to get rid of the arg and add the old var in, instead.
+    # See crbug.com/582737 for more on this. This can hopefully all
+    # go away with GYP.
+    m = re.search('llvm_force_head_revision=1\s*', gyp_defines)
+    if m:
+      env['LLVM_FORCE_HEAD_REVISION'] = '1'
+      gyp_defines = gyp_defines.replace(m.group(0), '')
+
+    # This is another terrible hack to work around the fact that
+    # GYP sets the link concurrency to use via the GYP_LINK_CONCURRENCY
+    # environment variable, and not via a proper GYP_DEFINE. See
+    # crbug.com/611491 for more on this.
+    m = re.search('gyp_link_concurrency=(\d+)(\s*)', gyp_defines)
+    if m:
+      env['GYP_LINK_CONCURRENCY'] = m.group(1)
+      gyp_defines = gyp_defines.replace(m.group(0), '')
+
+    env['GYP_GENERATORS'] = 'ninja'
+    if 'GYP_CHROMIUM_NO_ACTION' in env:
+      del env['GYP_CHROMIUM_NO_ACTION']
+    if 'GYP_CROSSCOMPILE' in env:
+      del env['GYP_CROSSCOMPILE']
+    env['GYP_DEFINES'] = gyp_defines
+    if vals['gyp_crosscompile']:
+      env['GYP_CROSSCOMPILE'] = '1'
+    return cmd, env
+
+  def RunGNAnalyze(self, vals):
+    # analyze runs before 'gn gen' now, so we need to run gn gen
+    # in order to ensure that we have a build directory.
+    ret = self.RunGNGen(vals)
+    if ret:
+      return ret
+
+    inp = self.ReadInputJSON(['files', 'test_targets',
+                              'additional_compile_targets'])
+    if self.args.verbose:
+      self.Print()
+      self.Print('analyze input:')
+      self.PrintJSON(inp)
+      self.Print()
+
+    # TODO(crbug.com/555273) - currently GN treats targets and
+    # additional_compile_targets identically since we can't tell the
+    # difference between a target that is a group in GN and one that isn't.
+    # We should eventually fix this and treat the two types differently.
+    targets = (set(inp['test_targets']) |
+               set(inp['additional_compile_targets']))
+
+    output_path = self.args.output_path[0]
+
+    # Bail out early if a GN file was modified, since 'gn refs' won't know
+    # what to do about it. Also, bail out early if 'all' was asked for,
+    # since we can't deal with it yet.
+    if (any(f.endswith('.gn') or f.endswith('.gni') for f in inp['files']) or
+        'all' in targets):
+      self.WriteJSON({
+            'status': 'Found dependency (all)',
+            'compile_targets': sorted(targets),
+            'test_targets': sorted(targets & set(inp['test_targets'])),
+          }, output_path)
+      return 0
+
+    # This shouldn't normally happen, but could due to unusual race conditions,
+    # like a try job that gets scheduled before a patch lands but runs after
+    # the patch has landed.
+    if not inp['files']:
+      self.Print('Warning: No files modified in patch, bailing out early.')
+      self.WriteJSON({
+            'status': 'No dependency',
+            'compile_targets': [],
+            'test_targets': [],
+          }, output_path)
+      return 0
+
+    ret = 0
+    response_file = self.TempFile()
+    response_file.write('\n'.join(inp['files']) + '\n')
+    response_file.close()
+
+    matching_targets = set()
+    try:
+      cmd = self.GNCmd('refs',
+                       self.args.path[0],
+                       '@%s' % response_file.name,
+                       '--all',
+                       '--as=output')
+      ret, out, _ = self.Run(cmd, force_verbose=False)
+      if ret and not 'The input matches no targets' in out:
+        self.WriteFailureAndRaise('gn refs returned %d: %s' % (ret, out),
+                                  output_path)
+      build_dir = self.ToSrcRelPath(self.args.path[0]) + self.sep
+      for output in out.splitlines():
+        build_output = output.replace(build_dir, '')
+        if build_output in targets:
+          matching_targets.add(build_output)
+
+      cmd = self.GNCmd('refs',
+                       self.args.path[0],
+                       '@%s' % response_file.name,
+                       '--all')
+      ret, out, _ = self.Run(cmd, force_verbose=False)
+      if ret and not 'The input matches no targets' in out:
+        self.WriteFailureAndRaise('gn refs returned %d: %s' % (ret, out),
+                                  output_path)
+      for label in out.splitlines():
+        build_target = label[2:]
+        # We want to accept 'chrome/android:chrome_public_apk' and
+        # just 'chrome_public_apk'. This may result in too many targets
+        # getting built, but we can adjust that later if need be.
+        for input_target in targets:
+          if (input_target == build_target or
+              build_target.endswith(':' + input_target)):
+            matching_targets.add(input_target)
+    finally:
+      self.RemoveFile(response_file.name)
+
+    if matching_targets:
+      self.WriteJSON({
+            'status': 'Found dependency',
+            'compile_targets': sorted(matching_targets),
+            'test_targets': sorted(matching_targets &
+                                   set(inp['test_targets'])),
+          }, output_path)
+    else:
+      self.WriteJSON({
+          'status': 'No dependency',
+          'compile_targets': [],
+          'test_targets': [],
+      }, output_path)
+
+    if self.args.verbose:
+      outp = json.loads(self.ReadFile(output_path))
+      self.Print()
+      self.Print('analyze output:')
+      self.PrintJSON(outp)
+      self.Print()
+
+    return 0
+
+  def ReadInputJSON(self, required_keys):
+    path = self.args.input_path[0]
+    output_path = self.args.output_path[0]
+    if not self.Exists(path):
+      self.WriteFailureAndRaise('"%s" does not exist' % path, output_path)
+
+    try:
+      inp = json.loads(self.ReadFile(path))
+    except Exception as e:
+      self.WriteFailureAndRaise('Failed to read JSON input from "%s": %s' %
+                                (path, e), output_path)
+
+    for k in required_keys:
+      if not k in inp:
+        self.WriteFailureAndRaise('input file is missing a "%s" key' % k,
+                                  output_path)
+
+    return inp
+
+  def WriteFailureAndRaise(self, msg, output_path):
+    if output_path:
+      self.WriteJSON({'error': msg}, output_path, force_verbose=True)
+    raise MBErr(msg)
+
+  def WriteJSON(self, obj, path, force_verbose=False):
+    try:
+      self.WriteFile(path, json.dumps(obj, indent=2, sort_keys=True) + '\n',
+                     force_verbose=force_verbose)
+    except Exception as e:
+      raise MBErr('Error %s writing to the output path "%s"' %
+                 (e, path))
+
+  def CheckCompile(self, master, builder):
+    url_template = self.args.url_template + '/{builder}/builds/_all?as_text=1'
+    url = urllib2.quote(url_template.format(master=master, builder=builder),
+                        safe=':/()?=')
+    try:
+      builds = json.loads(self.Fetch(url))
+    except Exception as e:
+      return str(e)
+    successes = sorted(
+        [int(x) for x in builds.keys() if "text" in builds[x] and
+          cmp(builds[x]["text"][:2], ["build", "successful"]) == 0],
+        reverse=True)
+    if not successes:
+      return "no successful builds"
+    build = builds[str(successes[0])]
+    step_names = set([step["name"] for step in build["steps"]])
+    compile_indicators = set(["compile", "compile (with patch)", "analyze"])
+    if compile_indicators & step_names:
+      return "compiles"
+    return "does not compile"
+
+  def PrintCmd(self, cmd, env):
+    if self.platform == 'win32':
+      env_prefix = 'set '
+      env_quoter = QuoteForSet
+      shell_quoter = QuoteForCmd
+    else:
+      env_prefix = ''
+      env_quoter = pipes.quote
+      shell_quoter = pipes.quote
+
+    def print_env(var):
+      if env and var in env:
+        self.Print('%s%s=%s' % (env_prefix, var, env_quoter(env[var])))
+
+    print_env('GYP_CROSSCOMPILE')
+    print_env('GYP_DEFINES')
+    print_env('GYP_LINK_CONCURRENCY')
+    print_env('LLVM_FORCE_HEAD_REVISION')
+
+    if cmd[0] == self.executable:
+      cmd = ['python'] + cmd[1:]
+    self.Print(*[shell_quoter(arg) for arg in cmd])
+
+  def PrintJSON(self, obj):
+    self.Print(json.dumps(obj, indent=2, sort_keys=True))
+
+  def GNTargetName(self, target):
+    return target
+
+  def Build(self, target):
+    build_dir = self.ToSrcRelPath(self.args.path[0])
+    ninja_cmd = ['ninja', '-C', build_dir]
+    if self.args.jobs:
+      ninja_cmd.extend(['-j', '%d' % self.args.jobs])
+    ninja_cmd.append(target)
+    ret, _, _ = self.Run(ninja_cmd, force_verbose=False, buffer_output=False)
+    return ret
+
+  def Run(self, cmd, env=None, force_verbose=True, buffer_output=True):
+    # This function largely exists so it can be overridden for testing.
+    if self.args.dryrun or self.args.verbose or force_verbose:
+      self.PrintCmd(cmd, env)
+    if self.args.dryrun:
+      return 0, '', ''
+
+    ret, out, err = self.Call(cmd, env=env, buffer_output=buffer_output)
+    if self.args.verbose or force_verbose:
+      if ret:
+        self.Print('  -> returned %d' % ret)
+      if out:
+        self.Print(out, end='')
+      if err:
+        self.Print(err, end='', file=sys.stderr)
+    return ret, out, err
+
+  def Call(self, cmd, env=None, buffer_output=True):
+    if buffer_output:
+      p = subprocess.Popen(cmd, shell=False, cwd=self.chromium_src_dir,
+                           stdout=subprocess.PIPE, stderr=subprocess.PIPE,
+                           env=env)
+      out, err = p.communicate()
+    else:
+      p = subprocess.Popen(cmd, shell=False, cwd=self.chromium_src_dir,
+                           env=env)
+      p.wait()
+      out = err = ''
+    return p.returncode, out, err
+
+  def ExpandUser(self, path):
+    # This function largely exists so it can be overridden for testing.
+    return os.path.expanduser(path)
+
+  def Exists(self, path):
+    # This function largely exists so it can be overridden for testing.
+    return os.path.exists(path)
+
+  def Fetch(self, url):
+    # This function largely exists so it can be overridden for testing.
+    f = urllib2.urlopen(url)
+    contents = f.read()
+    f.close()
+    return contents
+
+  def MaybeMakeDirectory(self, path):
+    try:
+      os.makedirs(path)
+    except OSError, e:
+      if e.errno != errno.EEXIST:
+        raise
+
+  def PathJoin(self, *comps):
+    # This function largely exists so it can be overriden for testing.
+    return os.path.join(*comps)
+
+  def Print(self, *args, **kwargs):
+    # This function largely exists so it can be overridden for testing.
+    print(*args, **kwargs)
+    if kwargs.get('stream', sys.stdout) == sys.stdout:
+      sys.stdout.flush()
+
+  def ReadFile(self, path):
+    # This function largely exists so it can be overriden for testing.
+    with open(path) as fp:
+      return fp.read()
+
+  def RelPath(self, path, start='.'):
+    # This function largely exists so it can be overriden for testing.
+    return os.path.relpath(path, start)
+
+  def RemoveFile(self, path):
+    # This function largely exists so it can be overriden for testing.
+    os.remove(path)
+
+  def RemoveDirectory(self, abs_path):
+    if self.platform == 'win32':
+      # In other places in chromium, we often have to retry this command
+      # because we're worried about other processes still holding on to
+      # file handles, but when MB is invoked, it will be early enough in the
+      # build that their should be no other processes to interfere. We
+      # can change this if need be.
+      self.Run(['cmd.exe', '/c', 'rmdir', '/q', '/s', abs_path])
+    else:
+      shutil.rmtree(abs_path, ignore_errors=True)
+
+  def TempFile(self, mode='w'):
+    # This function largely exists so it can be overriden for testing.
+    return tempfile.NamedTemporaryFile(mode=mode, delete=False)
+
+  def WriteFile(self, path, contents, force_verbose=False):
+    # This function largely exists so it can be overriden for testing.
+    if self.args.dryrun or self.args.verbose or force_verbose:
+      self.Print('\nWriting """\\\n%s""" to %s.\n' % (contents, path))
+    with open(path, 'w') as fp:
+      return fp.write(contents)
+
+
+class MBErr(Exception):
+  pass
+
+
+# See http://goo.gl/l5NPDW and http://goo.gl/4Diozm for the painful
+# details of this next section, which handles escaping command lines
+# so that they can be copied and pasted into a cmd window.
+UNSAFE_FOR_SET = set('^<>&|')
+UNSAFE_FOR_CMD = UNSAFE_FOR_SET.union(set('()%'))
+ALL_META_CHARS = UNSAFE_FOR_CMD.union(set('"'))
+
+
+def QuoteForSet(arg):
+  if any(a in UNSAFE_FOR_SET for a in arg):
+    arg = ''.join('^' + a if a in UNSAFE_FOR_SET else a for a in arg)
+  return arg
+
+
+def QuoteForCmd(arg):
+  # First, escape the arg so that CommandLineToArgvW will parse it properly.
+  # From //tools/gyp/pylib/gyp/msvs_emulation.py:23.
+  if arg == '' or ' ' in arg or '"' in arg:
+    quote_re = re.compile(r'(\\*)"')
+    arg = '"%s"' % (quote_re.sub(lambda mo: 2 * mo.group(1) + '\\"', arg))
+
+  # Then check to see if the arg contains any metacharacters other than
+  # double quotes; if it does, quote everything (including the double
+  # quotes) for safety.
+  if any(a in UNSAFE_FOR_CMD for a in arg):
+    arg = ''.join('^' + a if a in ALL_META_CHARS else a for a in arg)
+  return arg
+
+
+if __name__ == '__main__':
+  sys.exit(main(sys.argv[1:]))