Check the content setting type is valid.

BUG=169770
Review URL: https://codereview.chromium.org/11875013

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@176687 0039d316-1c4b-4281-b951-d872f2087c98
void TabSpecificContentSettings::SiteDataObserver::ContentSettingsDestroyed() {
  tab_specific_content_settings_ = NULL;
}

void TabSpecificContentSettings::SiteDataObserver::ContentSettingsDestroyed() {
  tab_specific_content_settings_ = NULL;
}
