Revert of Improve computation of PrefHashCalculator::legacy_device_id_instance_.

chrome/browser/prefs/pref_hash_calculator.cc

Index: chrome/browser/prefs/pref_hash_calculator.cc
diff --git a/chrome/browser/prefs/pref_hash_calculator.cc b/chrome/browser/prefs/pref_hash_calculator.cc
index 0a37aa58b9fb05854acff4965c8e4f75dd8c85ee..3fd951bcd237171ac5e783a51739b86eda49f58e 100644
--- a/chrome/browser/prefs/pref_hash_calculator.cc
+++ b/chrome/browser/prefs/pref_hash_calculator.cc
@@ -11,7 +11,6 @@
 #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"
@@ -92,10 +91,6 @@
 
 }  // namespace
 
-// static
-base::LazyInstance<scoped_ptr<const std::string> >::Leaky
-    PrefHashCalculator::legacy_device_id_instance_ = LAZY_INSTANCE_INITIALIZER;
-
 PrefHashCalculator::PrefHashCalculator(const std::string& seed,
                                        const std::string& device_id)
     : seed_(seed),
@@ -141,29 +136,10 @@
 }
 
 std::string PrefHashCalculator::RetrieveLegacyDeviceId() const {
-  scoped_ptr<const std::string>* legacy_device_id_ptr =
-      legacy_device_id_instance_.Pointer();
-  if (!legacy_device_id_ptr->get()) {
-    // 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 once in this browser's lifetime (as verified by the DCHECK
-    // below). 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. Another option would be to
-    // kick an early task on the FILE thread to start retrieving this ID on
-    // every startup and block here if the result still hasn't made it in when
-    // we need it, but this isn't great either as in most cases it will be
-    // computed for nothing.
-    // TODO(gab): Remove this when the legacy device ID (M33) becomes
-    // irrelevant.
-    base::ThreadRestrictions::ScopedAllowIO allow_io;
-    static bool legacy_device_id_computed = false;
-    DCHECK(!legacy_device_id_computed);
-    legacy_device_id_ptr->reset(
+  if (!legacy_device_id_instance_) {
+    legacy_device_id_instance_.reset(
         new std::string(GenerateDeviceIdLikePrefMetricsServiceDid(
             get_legacy_device_id_callback_.Run(raw_device_id_))));
-    legacy_device_id_computed = true;
   }
-  return *legacy_device_id_ptr->get();
+  return *legacy_device_id_instance_;
 }