function updateDirtyFilesCache(name, action) {
    if (action) {
        _dirtyFilesCache[name] = true;
    } else {
        if (_dirtyFilesCache[name]) {
            delete _dirtyFilesCache[name];
        }
    }
}
Updates the files cache with fullpath when dirty flag changes for a document
If the doc is being marked as dirty then an entry is created in the cache
If the doc is being marked as clean then the corresponsing entry gets cleared from cache

@param {String} name - fullpath of the document
@param {boolean} action - whether the document is dirty