Move variations prefs into the variations component

These prefs are used by variations code that is targeted for componentization.

BUG=382865
TBR=thakis

Review URL: https://codereview.chromium.org/1265423003

Cr-Commit-Position: refs/heads/master@{#343661}
void VariationsService::StartRepeatedVariationsSeedFetch() {
  DCHECK(thread_checker_.CalledOnValidThread());

  variations_server_url_ =
      GetVariationsServerURL(policy_pref_service_, restrict_mode_);

  DCHECK(create_trials_from_seed_called_);

  DCHECK(!request_scheduler_.get());
  request_scheduler_.reset(VariationsRequestScheduler::Create(
      base::Bind(&VariationsService::FetchVariationsSeed,
                 weak_ptr_factory_.GetWeakPtr()),
      local_state_));
  request_scheduler_->Start();
}

void VariationsService::StartRepeatedVariationsSeedFetch() {
  DCHECK(thread_checker_.CalledOnValidThread());

  variations_server_url_ =
      GetVariationsServerURL(policy_pref_service_, restrict_mode_);

  DCHECK(create_trials_from_seed_called_);

  DCHECK(!request_scheduler_.get());
  request_scheduler_.reset(VariationsRequestScheduler::Create(
      base::Bind(&VariationsService::FetchVariationsSeed,
                 weak_ptr_factory_.GetWeakPtr()),
      local_state_));
  request_scheduler_->Start();
}
