Don't set cpu architecture field on iOS in UMA logs.

components/metrics/metrics_log_unittest.cc

 // 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 "components/metrics/metrics_log.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <string>
@@ skipping 177 matching lines @@
   SystemProfileProto* system_profile = expected.mutable_system_profile();
   system_profile->set_app_version("bogus version");
   system_profile->set_channel(client.GetChannel());
   system_profile->set_application_locale(client.GetApplicationLocale());
 
 #if defined(SYZYASAN)
   system_profile->set_is_asan_build(true);
 #endif
   metrics::SystemProfileProto::Hardware* hardware =
       system_profile->mutable_hardware();
+#if !defined(OS_IOS)
   hardware->set_cpu_architecture(base::SysInfo::OperatingSystemArchitecture());
+#endif
   hardware->set_system_ram_mb(base::SysInfo::AmountOfPhysicalMemoryMB());
   hardware->set_hardware_class(base::SysInfo::HardwareModelName());
 #if defined(OS_WIN)
   hardware->set_dll_base(reinterpret_cast<uint64_t>(CURRENT_MODULE()));
 #endif
 
   system_profile->mutable_os()->set_name(base::SysInfo::OperatingSystemName());
   system_profile->mutable_os()->set_version(
       base::SysInfo::OperatingSystemVersion());
 #if defined(OS_ANDROID)
@@ skipping 288 matching lines @@
   TestMetricsServiceClient client;
   client.set_product(kTestProduct);
   TestMetricsLog log(
       kClientId, kSessionId, MetricsLog::ONGOING_LOG, &client, &prefs_);
   // Check that the product is set to |kTestProduct|.
   EXPECT_TRUE(log.uma_proto().has_product());
   EXPECT_EQ(kTestProduct, log.uma_proto().product());
 }
 
 }  // namespace metrics