Add the ability to pass use flags through cbuildbot to build_packages.

buildbot/cbuildbot_stages.py

 # Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Module containing the various stages that a builder runs."""
 
 import os
 import re
 import sys
 import tempfile
@@ skipping 301 matching lines @@
 
 class BuildTargetStage(BuilderStage):
   """This stage builds Chromium OS for a target.
 
   Specifically, we build Chromium OS packages and perform imaging to get
   the images we want per the build spec."""
   def _PerformStage(self):
     BuilderStage.new_binhost = self._GetPortageEnvVar(_FULL_BINHOST)
     emptytree = (BuilderStage.old_binhost and
                  BuilderStage.old_binhost != BuilderStage.new_binhost)
+    env=[]
+    if self._build_config['useflags']:
+      env.append('USE="%s"' % ' '.join(self._build_config['useflags']))
 
     commands.Build(
         self._build_root, emptytree, usepkg=self._build_config['usepkg'],
-        build_autotest=(self._build_config['vm_tests'] and self._options.tests))
+        build_autotest=(self._build_config['vm_tests'] and self._options.tests),
+        extra_env=env)
 
     # TODO(sosa):  Do this optimization in a better way.
     if self._build_type == 'full':
       commands.UploadPrebuilts(
           self._build_root, self._build_config['board'],
           self._build_config['rev_overlays'], [], self._build_type,
           False)
 
     commands.BuildImage(self._build_root)
 
@@ skipping 56 matching lines @@
   def _PerformStage(self):
     if self._build_type in ('preflight', 'chrome'):
       commands.UploadPrebuilts(
           self._build_root, self._build_config['board'],
           self._build_config['rev_overlays'], [BuilderStage.new_binhost],
           self._build_type, self._options.chrome_rev)
 
     commands.UprevPush(self._build_root, self._options.tracking_branch,
                        self._build_config['board'], BuilderStage.push_overlays,
                        self._options.debug)