Fix protobuf's Python runtime and imports.

third_party/dom_distiller_js/protoc_plugins/util/plugin_protos.py

 # Copyright 2016 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.
 
 """
 Provides simple state-less wrappers of the proto types used by plugins.
 
 See https://developers.google.com/protocol-buffers/docs/reference/cpp/google.protobuf.descriptor.pb
 and https://developers.google.com/protocol-buffers/docs/reference/cpp/google.protobuf.compiler.plugin.pb
 """
 
 import os
 import sys
 
-SCRIPT_DIR = os.path.dirname(__file__)
-SRC_DIR = os.path.abspath(os.path.join(SCRIPT_DIR, '..', '..', '..', '..'))
+PYPROTO_DIR = os.path.abspath('pyproto')
+sys.path.insert(0, PYPROTO_DIR)
+import google.protobuf
 
-sys.path.insert(
-    1, os.path.join(SRC_DIR, 'third_party', 'protobuf', 'python'))
-sys.path.insert(
-    1, os.path.join(SRC_DIR, 'third_party', 'protobuf', 'third_party', 'six'))
+FOO = os.path.abspath( \
+  os.path.join(os.path.dirname(google.protobuf.__file__), '..', '..'))
+if PYPROTO_DIR != FOO:
+  print >> sys.stderr, 'PYPROTO_DIR = ' + PYPROTO_DIR
+  print >> sys.stderr, 'FOO = ' + FOO
+  assert False
+
+from google.protobuf.compiler import plugin_pb2
 from google.protobuf.descriptor_pb2 import FieldDescriptorProto
 
 from . import types
 
-sys.path.insert(
-    1, os.path.join(SRC_DIR,
-                    'third_party', 'dom_distiller_js', 'dist', 'python'))
-import plugin_pb2
-
 
 class PluginRequest(object):
   def __init__(self, proto):
     self.proto = proto
 
   def GetArgs(self):
     return dict((v.split('=') for v in self.proto.parameter.split(',')))
 
   def GetAllFiles(self):
     files = map(ProtoFile, self.proto.proto_file)
@@ skipping 242 matching lines @@
   def GetName(self):
     return self.proto.name
 
   def GetValue(self):
     return self.proto.number
 
   def CheckSupported(self):
     if self.proto.HasField('options'):
       return 'Enum value options are not supported: {} {}'.format(
           self.proto.name, self.proto.value)