[Cronet] Export NSError constants instead of defining them in Cronet.h

components/cronet/ios/Cronet.mm

 // 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.
 
 #import "components/cronet/ios/Cronet.h"
 
 #include <memory>
 #include <vector>
 
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/mac/bundle_locations.h"
 #include "base/mac/scoped_block.h"
 #include "base/memory/ptr_util.h"
 #include "base/strings/sys_string_conversions.h"
 #include "base/synchronization/lock.h"
 #include "components/cronet/ios/accept_languages_table.h"
 #include "components/cronet/ios/cronet_environment.h"
 #include "components/cronet/url_request_context_config.h"
 #include "ios/net/crn_http_protocol_handler.h"
 #include "ios/net/empty_nsurlcache.h"
 #include "net/cert/cert_verifier.h"
 #include "net/url_request/url_request_context_getter.h"
 
+// Cronet NSError constants.
+NSString* const CRNCronetErrorDomain = @"CRNCronetErrorDomain";
+NSString* const CRNInvalidArgumentKey = @"CRNInvalidArgumentKey";
+
 namespace {
 
 class CronetHttpProtocolHandlerDelegate;
 
 using QuicHintVector =
     std::vector<std::unique_ptr<cronet::URLRequestContextConfig::QuicHint>>;
 // Currently there is one and only one instance of CronetEnvironment,
 // which is leaked at the shutdown. We should consider allowing multiple
 // instances if that makes sense in the future.
 base::LazyInstance<std::unique_ptr<cronet::CronetEnvironment>>::Leaky
@@ skipping 378 matching lines @@
 }
 
 + (NSError*)createCronetErrorWith:(int)errorCode
                          userInfo:(NSDictionary*)userInfo {
   return [NSError errorWithDomain:CRNCronetErrorDomain
                              code:errorCode
                          userInfo:userInfo];
 }
 
 @end