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}
MasterPreferences::MasterPreferences(const base::CommandLine& cmd_line)
    : distribution_(NULL),
      preferences_read_from_file_(false),
      chrome_(true),
      multi_install_(false) {
  InitializeFromCommandLine(cmd_line);
}

MasterPreferences::MasterPreferences(const base::CommandLine& cmd_line)
    : distribution_(NULL),
      preferences_read_from_file_(false),
      chrome_(true),
      multi_install_(false) {
  InitializeFromCommandLine(cmd_line);
}
