CloudFront HTTP headers

I'd like to analyze the number of requests, for example, that contain the HTTP headers that I've included in my CloudFront cache key. How can I do this? For example, when I created my caching policy, I enabled the CloudFront-Is-Mobile/SmartTV/Desktop-Viewer headers because I'd like to see how many requests originate from these different device types. I thought the HTTP header information would be available in CloudFront standard logs, but no such luck. Where to look?