function getRichItemNames(textStyleModel) {
    // Use object to remove duplicated names.
    var richItemNameMap;
    while (textStyleModel && textStyleModel !== textStyleModel.ecModel) {
        var rich = (textStyleModel.option || EMPTY_OBJ).rich;
        if (rich) {
            richItemNameMap = richItemNameMap || {};
            for (var name in rich) {
                if (rich.hasOwnProperty(name)) {
                    richItemNameMap[name] = 1;
                }
            }
        }
        textStyleModel = textStyleModel.parentModel;
    }
    return richItemNameMap;
}
Give some default value to the input `textStyle` object, based on the current settings
in this `textStyle` object.

The Scenario:
when text position is `inside` and `textFill` is not specified, we show
text border by default for better view. But it should be considered that text position
might be changed when hovering or being emphasis, where the `insideRollback` is used to
restore the style.

Usage (& NOTICE):
When a style object (eithor plain object or instance of `zrender/src/graphic/Style`) is
about to be modified on its text related properties, `rollbackDefaultTextStyle` should
be called before the modification and `applyDefaultTextStyle` should be called after that.
(For the case that all of the text related properties is reset, like `setTextStyleCommon`
does, `rollbackDefaultTextStyle` is not needed to be called).