css_combine overly pessimistic (should combine even if CSS cannot be fully parsed)

[GoogleCodeExporter]

With the new 1.1.23.1-beta release, I'm seeing various entries like these in my 
log:

[info] [mod_pagespeed 1.1.23.1-2169 @20563] Failed to combine 
https://www.example.com/wp-admin/css/wp-admin.css?ver=3.4.2 because of parse 
error.
[info] [mod_pagespeed 1.1.23.1-2169 @20563] Cannot combine: not combinable

It appears that some CSS 3 syntax is still not supported.

----

 $ wget http://core.trac.wordpress.org/export/22550/tags/3.4.2/wp-admin/css/wp-admin.dev.css
 $ /usr/local/src/modpagespeed/src/out/Release/css_minify_main wp-admin.dev.css > /dev/null
 # /usr/local/src/modpagespeed/src/out/Release/css_minify_main wp-admin.dev.css > /dev/null
 CSS unparseable sections mask 134
 Ignoring chars in value. at byte 91346 "...ition-property: left, right, top, bottom..."
 Failed to parse values for property -webkit-transition-property at byte 91347 "...tion-property: left, right, top, bottom,..."
 Ignoring chars in value. at byte 91417 "...on-property:    left, right, top, bottom..."
 Failed to parse values for property -moz-transition-property at byte 91418 "...n-property:    left, right, top, bottom,..."
 Ignoring chars in value. at byte 91488 "...n-property:     left, right, top, bottom..."
 Failed to parse values for property -ms-transition-property at byte 91489 "...-property:     left, right, top, bottom,..."
 Ignoring chars in value. at byte 91559 "...-property:      left, right, top, bottom..."
 Failed to parse values for property -o-transition-property at byte 91560 "...property:      left, right, top, bottom,..."
 Ignoring chars in value. at byte 91630 "...operty:         left, right, top, bottom..."
 Failed to parse values for property transition-property at byte 91631 "...perty:         left, right, top, bottom,..."
 Could not parse selector: illegal char ~ at byte 127470 "...en;
 }

 input.newtag ~ div.taghint {
         vis..."
 Failed to parse selector at byte 127484 "...ewtag ~ div.taghint {
         visibility: visib..."
 Could not parse selector: illegal char ~ at byte 127530 "...
 input.newtag:focus ~ div.taghint {
         vis..."
 Failed to parse selector at byte 127544 "...focus ~ div.taghint {
         visibility: hidde..."

... and also ...

 $ wget http://core.trac.wordpress.org/export/22550/tags/3.4.2/wp-includes/css/admin-bar.dev.css
 $ /usr/local/src/modpagespeed/src/out/Release/css_minify_main admin-bar.dev.css > /dev/null
 CSS unparseable sections mask 130
 Ignoring chars in value. at byte 10314 "...tion-property: width, background;
         -webk..."
 Failed to parse values for property -webkit-transition-property at byte 10315 "...ion-property: width, background;
         -webki..."
 Ignoring chars in value. at byte 10437 "...tion-property: width, background;
         -moz-..."
 Failed to parse values for property -moz-transition-property at byte 10438 "...ion-property: width, background;
         -moz-t..."
 Ignoring chars in value. at byte 10553 "...tion-property: width, background;
         -o-tr..."
 Failed to parse values for property -o-transition-property at byte 10554 "...ion-property: width, background;
         -o-tra..."

----

Reference issue 108.

Original issue reported on code.google.com by amat...@gmail.com on 12 Nov 2012 at 10:56