Add search_engines and precache components to GN build.

build/json_to_struct.gypi

 # Copyright 2012 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.
 
 {
   'variables': {
     # When including this gypi, the following variables must be set:
     #   schema_file: a json file that comprise the structure model.
     #   namespace: the C++ namespace that all generated files go under
     #   cc_dir: path to generated files
     # Functions and namespaces can be excluded by setting "nocompile" to true.
     'struct_gen_dir': '<(DEPTH)/tools/json_to_struct',
     'struct_gen': '<(struct_gen_dir)/json_to_struct.py',
   },
   'rules': [
     {
+      # GN version: //tools/json_to_struct/json_to_struct.gni
       'rule_name': 'genstaticinit',
       'extension': 'json',
       'inputs': [
         '<(struct_gen_dir)/element_generator.py',
         '<(struct_gen_dir)/json_to_struct.py',
         '<(struct_gen_dir)/struct_generator.py',
         '<(schema_file)',
       ],
       'outputs': [
         '<(SHARED_INTERMEDIATE_DIR)/<(cc_dir)/<(RULE_INPUT_ROOT).cc',
@@ skipping 13 matching lines @@
     },
   ],
   'include_dirs': [
     '<(SHARED_INTERMEDIATE_DIR)',
     '<(DEPTH)',
   ],
   # This target exports a hard dependency because it generates header
   # files.
   'hard_dependency': 1,
 }