Fix protobuf's Python runtime and imports.

third_party/protobuf/proto_library.gni

 # 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.
 
 # Compile a protocol buffer.
 #
 # Protobuf parameters:
 #
 #   proto_in_dir (optional)
 #       Specifies the path relative to the current BUILD.gn file where
@@ skipping 309 matching lines @@
       invoker.component_build_force_source_set && is_component_build) {
     link_target_type = "source_set"
   } else {
     link_target_type = "static_library"
   }
 
   # Generated files may include other generated headers. These includes always
   # use relative paths starting at |cc_out_dir|.
   # However there is no necessity to add an additional directory, if all protos
   # are located in the same directory which is in the search path by default.
-  if (has_nested_dirs) {
+  if (has_nested_dirs && (generate_cc || generate_with_plugin)) {
     config_name = "${target_name}_config"
     config(config_name) {
       include_dirs = [ cc_out_dir ]
     }
   }
 
   # Build generated protobuf stubs as libary or source set.
   target(link_target_type, target_name) {
     forward_variables_from(invoker,
                            [
@@ skipping 49 matching lines @@
       ":$action_name",
     ]
 
     # This will link any libraries in the deps (the use of invoker.deps in the
     # action won't link it).
     if (defined(invoker.deps)) {
       deps += invoker.deps
     }
   }
 }