"ModPagespeedImplicitCacheTtlMs " directive doesn't work in IPRO mode

[GoogleCodeExporter]

I'm using "mod_pagespeed 1.7.30.2-3702" beta version. 

"ModPagespeedImplicitCacheTtlMs " directive doesn't work in IPRO mode.
If the origin website doesn't specify a timeout (neither Expires nor 
Cache-Control), IPRO will be append a http header "Cache-Control: max-age=300" 
anyway, no matter what the "ImplicitCacheTttlMs" is set.

jmarantz@google.com said:
"
I think the correct behavior is that we should not put any extra cache headers 
in ipro-optimized responses, and that this might be a bug. 

We still need to use the implicit cache ttl to help tune the interval we check 
for updates at origin.  Otherwise we will add an extra round-trip to origin to 
do cache validation, which will increase latency.

However I think we *do* want to add a header (usually 
cache-control:max-age=300,private) when mod_pagespeed serves a 
not-yet-optimized resource.  This should occur only transiently while 
mod_pagespeeed optimizes the resource in the background.
"


Refer to:
https://groups.google.com/forum/#!topic/mod-pagespeed-discuss/yKJ-2bRKS7U

Original issue reported on code.google.com by centiped...@gmail.com on 10 Jan 2014 at 9:06