Tests download is canceled when behavior is set to deny.
Downloading via a navigation: 
{
    method : Page.downloadWillBegin
    params : {
        frameId : <string>
        guid : <string>
        suggestedFilename : hello.txt
        url : http://127.0.0.1:8000/devtools/network/resources/resource.php?download=1
    }
    sessionId : <string>
}
{
    method : Page.downloadProgress
    params : {
        guid : <string>
        receivedBytes : <number>
        state : inProgress
        totalBytes : 11
    }
    sessionId : <string>
}
{
    method : Page.downloadProgress
    params : {
        guid : <string>
        receivedBytes : <number>
        state : canceled
        totalBytes : 11
    }
    sessionId : <string>
}
Downloading by clicking a link: 
{
    method : Page.downloadWillBegin
    params : {
        frameId : <string>
        guid : <string>
        suggestedFilename : hello.text
        url : http://127.0.0.1:8000/devtools/network/resources/resource.php
    }
    sessionId : <string>
}
{
    method : Page.downloadProgress
    params : {
        guid : <string>
        receivedBytes : <number>
        state : inProgress
        totalBytes : 11
    }
    sessionId : <string>
}
{
    method : Page.downloadProgress
    params : {
        guid : <string>
        receivedBytes : <number>
        state : canceled
        totalBytes : 11
    }
    sessionId : <string>
}