[Cronet] Add BUILD.gn for legacy ios/CrNet project.

ios/crnet/crnet_environment.mm

 // 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.
 
 #include "ios/crnet/crnet_environment.h"
 
 #import <Foundation/Foundation.h>
 
 #include <utility>
 
 #include "base/at_exit.h"
 #include "base/atomicops.h"
 #include "base/command_line.h"
 #include "base/feature_list.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/files/scoped_file.h"
-#include "base/i18n/icu_util.h"
 #include "base/json/json_writer.h"
 #include "base/mac/bind_objc_block.h"
 #include "base/mac/bundle_locations.h"
 #include "base/mac/foundation_util.h"
 #include "base/mac/scoped_block.h"
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
 #include "base/metrics/statistics_recorder.h"
 #include "base/path_service.h"
 #include "base/single_thread_task_runner.h"
@@ skipping 29 matching lines @@
 #include "net/url_request/data_protocol_handler.h"
 #include "net/url_request/file_protocol_handler.h"
 #include "net/url_request/sdch_dictionary_fetcher.h"
 #include "net/url_request/static_http_user_agent_settings.h"
 #include "net/url_request/url_request_context_getter.h"
 #include "net/url_request/url_request_context_storage.h"
 #include "net/url_request/url_request_job_factory_impl.h"
 #include "url/url_features.h"
 #include "url/url_util.h"
 
+#if !BUILDFLAG(USE_PLATFORM_ICU_ALTERNATIVES)
+#include "base/i18n/icu_util.h"  // nogncheck
+#endif
+
 namespace {
 
 base::AtExitManager* g_at_exit_ = nullptr;
 
 // Request context getter for CrNet.
 class CrNetURLRequestContextGetter : public net::URLRequestContextGetter {
  public:
   CrNetURLRequestContextGetter(
       net::URLRequestContext* context,
       const scoped_refptr<base::SingleThreadTaskRunner>& task_runner)
@@ skipping 412 matching lines @@
 
   return user_agent_settings->GetUserAgent();
 }
 
 void CrNetEnvironment::ClearCache(ClearCacheCallback callback) {
   PostToNetworkThread(
       FROM_HERE,
       base::Bind(&net::ClearHttpCache, main_context_getter_,
                  network_io_thread_->task_runner(), base::BindBlock(callback)));
 }