Allow IO for the computation of PrefHashCalculator::legacy_device_id_instance_.

chrome/browser/prefs/pref_hash_calculator.cc

 // Copyright 2013 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 "chrome/browser/prefs/pref_hash_calculator.h"
 
 #include <vector>
 
 #include "base/bind.h"
 #include "base/json/json_string_value_serializer.h"
 #include "base/logging.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
+#include "base/threading/thread_restrictions.h"
 #include "base/values.h"
 #include "chrome/browser/prefs/tracked/pref_hash_calculator_helper.h"
 #include "crypto/hmac.h"
 
 namespace {
 
 // Calculates an HMAC of |message| using |key|, encoded as a hexadecimal string.
 std::string GetDigestString(const std::string& key,
                             const std::string& message) {
   crypto::HMAC hmac(crypto::HMAC::SHA256);
@@ skipping 106 matching lines @@
                          digest_string)) {
     return VALID_SECURE_LEGACY;
   }
   if (VerifyDigestString(seed_, value_as_string, digest_string))
     return VALID_WEAK_LEGACY;
   return INVALID;
 }
 
 std::string PrefHashCalculator::RetrieveLegacyDeviceId() const {
   if (!legacy_device_id_instance_) {
+    // Allow IO on this thread to retrieve the legacy device ID. The result of
+    // this operation is stored in |legacy_device_id_instance_| and will thus
+    // only happen at most once per PrefHashCalculator. This is not ideal, but
+    // this value is required synchronously to be able to continue loading prefs
+    // for this profile. This profile should then be migrated to a modern device
+    // ID and subsequent loads of this profile shouldn't need to run this code
+    // ever again.
+    // TODO(gab): Remove this when the legacy device ID (M33) becomes
+    // irrelevant.
+    base::ThreadRestrictions::ScopedAllowIO allow_io;
     legacy_device_id_instance_.reset(
         new std::string(GenerateDeviceIdLikePrefMetricsServiceDid(
             get_legacy_device_id_callback_.Run(raw_device_id_))));
   }
   return *legacy_device_id_instance_;
 }