Pref service: enable for user prefs in chrome behind a flag.

services/preferences/public/cpp/persistent_pref_store_client.cc

 // Copyright 2017 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 "services/preferences/public/cpp/persistent_pref_store_client.h"
 
 #include <utility>
 
+#include "base/threading/thread_restrictions.h"
 #include "base/values.h"
+#include "mojo/public/cpp/bindings/sync_call_restrictions.h"
 
 namespace prefs {
 
 PersistentPrefStoreClient::PersistentPrefStoreClient(
     mojom::PersistentPrefStoreConnectorPtr connector)
     : connector_(std::move(connector)) {}
 
 void PersistentPrefStoreClient::SetValue(const std::string& key,
                                          std::unique_ptr<base::Value> value,
                                          uint32_t flags) {
@@ skipping 43 matching lines @@
     const {
   return read_error_;
 }
 
 PersistentPrefStore::PrefReadError PersistentPrefStoreClient::ReadPrefs() {
   PrefReadError read_error = PrefReadError::PREF_READ_ERROR_NONE;
   bool read_only = false;
   std::unique_ptr<base::DictionaryValue> local_prefs;
   mojom::PersistentPrefStorePtr pref_store;
   mojom::PrefStoreObserverRequest observer_request;
+  base::ThreadRestrictions::AssertWaitAllowed();

[jam, 2017/03/22 14:58:12]

nit: curious why you added this? mojo::SyncCallRestrictions already has a
ScopedAllowWait member. I think no need to worry about both restrictions, just
the mojo one.

[Sam McNally, 2017/03/28 23:06:22]

It was intended to detect inadvertent post-startup sync pref creation. Removed
it.

+  mojo::SyncCallRestrictions::ScopedAllowSyncCall allow_sync_calls;
   if (!connector_->Connect(&read_error, &read_only, &local_prefs, &pref_store,
                            &observer_request)) {
     NOTREACHED();
   }
 
   OnCreateComplete(read_error, read_only, std::move(local_prefs),
                    std::move(pref_store), std::move(observer_request));
   return read_error_;
 }
 
@@ skipping 37 matching lines @@
   read_only_ = read_only;
   pref_store_ = std::move(pref_store);
   if (error_delegate_ && read_error_ != PREF_READ_ERROR_NONE)
     error_delegate_->OnError(read_error_);
   error_delegate_.reset();
 
   Init(std::move(cached_prefs), true, std::move(observer_request));
 }
 
 }  // namespace prefs