if (!mRules) { nsresult rv = NS_NewISupportsArray(getter_AddRefs(mRules)); if (NS_FAILED(rv)) return rv; }
CSSMediaRuleImpl::InsertRule(nsAReadableString & aRule, PRUint32 aIndex, PRUint32* _retval){  NS_ENSURE_TRUE(mSheet, NS_ERROR_FAILURE);  NS_ENSURE_TRUE(mRules, NS_ERROR_FAILURE);    PRUint32 count;  mRules->Count(&count);  if (aIndex > count)    return NS_ERROR_DOM_INDEX_SIZE_ERR;    return mSheet->InsertRuleIntoGroup(aRule, this, aIndex, _retval);}