Permit webp images as an input format

[GoogleCodeExporter]

mod_pagespeed should permit the use of webp images on the server side, 
converting them to jpg or png if the target browser doesn't support webp.

Note that this basically requires the server to be running mod_pagespeed all 
the time, as turning it off will yield pages that break non-webp browsers.  But 
it's likely to save a lot of bytes on the server, and webp->jpg conversion is 
(I think) faster than jpeg->webp.

Original issue reported on code.google.com by jmaes...@google.com on 16 Jul 2013 at 8:33

[GoogleCodeExporter]

What if we can't rewrite and render within 10ms?  What if it's a page with 100+ 
webp images?

Original comment by jkar...@google.com on 17 Jul 2013 at 11:06

[GoogleCodeExporter]

Ah, you're worried about fallback for non-webp-capable browsers.  That's a good 
point, it's in that respect different from our normal image flow (where failure 
to optimize still serves correct content).  That makes this a longer-term 
project than I thought.

Original comment by jmaes...@google.com on 17 Jul 2013 at 2:59

[GoogleCodeExporter]

It sounds like there are two aspects of this feature request:

1) Be able to parse .webp and do something with them. I think everyone is in 
support of this.

2) Encourage people to use .webp instead of .jpg and depend on mod_pagespeed to 
fix them appropriately for browsers. That will change a lot of assumptions 
we've had about it being OK to not rewrite things and turning mod_pagespeed off 
to be safe, etc. And might need more discussion.

Original comment by sligocki@google.com on 17 Jul 2013 at 3:04