[Android Buildbot] Add option to set extra env vars before envsetup.

build/android/buildbot/bb_run_bot.py

Index: build/android/buildbot/bb_run_bot.py
diff --git a/build/android/buildbot/bb_run_bot.py b/build/android/buildbot/bb_run_bot.py
index 23db7ec2ba3d5265f05dbc1f4d51238e2cb00b46..9e2efbe5df4d6456ae44c10294b6bc70e0fbbf60 100755
--- a/build/android/buildbot/bb_run_bot.py
+++ b/build/android/buildbot/bb_run_bot.py
@@ -45,10 +45,12 @@ def DictDiff(d1, d2):
   return '\n'.join(diff)
 
 
-def GetEnvironment(host_obj, testing):
+def GetEnvironment(host_obj, testing, extra_env_vars=None):
   init_env = dict(os.environ)
   init_env['GYP_GENERATORS'] = 'ninja'
   init_env['GOMA_DIR'] = bb_utils.GOMA_DIR
+  if extra_env_vars:
+    init_env.update(extra_env_vars)
   envsetup_cmd = '. build/android/envsetup.sh'
   if host_obj.target_arch:
     envsetup_cmd += ' --target-arch=%s' % host_obj.target_arch