DevTools: move front-end URL handling to DevToolsUIBindingds

BUG=662859

Review-Url: https://codereview.chromium.org/2607833002
Cr-Commit-Position: refs/heads/master@{#440926}
void DevToolsUIBindings::ClearPreferences() {
  DictionaryPrefUpdate update(profile_->GetPrefs(),
                              prefs::kDevToolsPreferences);
  update.Get()->Clear();
}

void DevToolsUIBindings::ClearPreferences() {
  DictionaryPrefUpdate update(profile_->GetPrefs(),
                              prefs::kDevToolsPreferences);
  update.Get()->Clear();
}
