Added virtualenv for depot_tools

bootstrap/custom_builds/protobuf.py

Index: bootstrap/custom_builds/protobuf.py
diff --git a/bootstrap/custom_builds/protobuf.py b/bootstrap/custom_builds/protobuf.py
new file mode 100644
index 0000000000000000000000000000000000000000..8a483fd8f817027f97555717b67c6c4d7a95ea89
--- /dev/null
+++ b/bootstrap/custom_builds/protobuf.py
@@ -0,0 +1,22 @@
+# Copyright 2014 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 os
+import subprocess
+import sys
+
+
+def Build(source_path, wheelhouse_path):
+  # First, have to compile the protoc executable. Note that this
+  # 1) only runs on unix-like systems, and
+  # 2) requires autoconf and libtool to be installed (e.g. via apt-get).
+  subprocess.check_call(['./autogen.sh'], cwd=source_path)
+  subprocess.check_call(['./configure'], cwd=source_path)
+  subprocess.check_call(['make'], cwd=source_path)
+
+  # Now that we have <source_path>/src/protoc, we can build the python package.
+  cwd = os.path.join(source_path, 'python')
+  subprocess.check_call(
+      ['python', 'setup.py', 'bdist_wheel', '--dist-dir', wheelhouse_path],
+      cwd=cwd)