Tests file download.
Setting download behavior to allow...
Downloading file by clicking an anchor link...
Browser.downloadWillBegin: {
    method : Browser.downloadWillBegin
    params : {
        frameId : <string>
        guid : <string>
        suggestedFilename : download.txt
        url : data:text/plain;charset=utf-8,Hello_headless_world!
    }
    sessionId : <string>
}
Browser.downloadProgress: {
    method : Browser.downloadProgress
    params : {
        filePath : <string>
        guid : <string>
        receivedBytes : <number>
        state : completed
        totalBytes : 21
    }
    sessionId : <string>
}
Downloaded file path: <some file path>/download.txt