[Android] Refactor bb_host_steps to prepare for downstream usage.

build/android/buildbot/bb_utils.py

 # Copyright 2013 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.
 
 import json
 import optparse
 import os
 import pipes
 import subprocess
 import sys
@@ skipping 58 matching lines @@
                     help='build properties in JSON format')
   parser.add_option('--factory-properties', action='callback',
                     callback=ConvertJson, type='string', default={},
                     help='factory properties in JSON format')
   return parser
 
 
 def EncodeProperties(options):
   return ['--factory-properties=%s' % json.dumps(options.factory_properties),
           '--build-properties=%s' % json.dumps(options.build_properties)]
+
+
+def RunSteps(all_steps, options):
+  if not options.steps:
+    return
+
+  steps = options.steps.split(',')
+  unknown_steps = set(steps) - set(step for step, _ in all_steps)
+  if unknown_steps:
+    print >> sys.stderr, 'FATAL: Unknown steps %s' % list(unknown_steps)
+    sys.exit(1)
+
+  for step, cmd in all_steps:
+    if step in steps:
+      cmd(options)