Local font source is not recognized as valid

[Andrey Savchenko]

Only font faces having src: url() are treated as valid, so src: local() ones would always be considered invalid and dropped, even if they are detected as critical fonts.

@font-face {
  font-family: "Alegreya-fallback";
  size-adjust: 101%;
  src: local("Times New Roman");
}

critters/packages/critters/src/index.js

Lines 568 to 587 in a590c05

     src = (decl.value.match(/url\s*\(\s*(['"]?)(.+?)\1\s*\)/) || [])[2]; 
   } else if (decl.prop === 'font-family') { 
     family = decl.value; 
   } 
 } 
  
 if (src && shouldPreloadFonts && preloadedFonts.indexOf(src) === -1) { 
   preloadedFonts.push(src); 
   const preload = document.createElement('link'); 
   preload.setAttribute('rel', 'preload'); 
   preload.setAttribute('as', 'font'); 
   preload.setAttribute('crossorigin', 'anonymous'); 
   preload.setAttribute('href', src.trim()); 
   document.head.appendChild(preload); 
 } 
  
 // if we're missing info, if the font is unused, or if critical font inlining is disabled, remove the rule: 
 if ( 
   !family || 
   !src || 

Related #112