[css-properties-values-api] List syntaxes should accept one or more items.

Currently we accept zero items, which is wrong.

R=futhark@chromium.org

Bug: 641877
Change-Id: I8acdc4c5c7ba54a71a478e7eed79223271e1e92d
Reviewed-on: https://chromium-review.googlesource.com/c/1290889Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Anders Ruud <andruud@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601128}

third_party/WebKit/LayoutTests/external/wpt/css/css-properties-values-api/register-property-syntax-parsing-expected.txt

 This is a testharness.js-based test.
-Found 130 tests; 129 PASS, 1 FAIL, 0 TIMEOUT, 0 NOTRUN.
+Found 133 tests; 132 PASS, 1 FAIL, 0 TIMEOUT, 0 NOTRUN.
 PASS syntax:'*', initialValue:'a' is valid
 PASS syntax:' * ', initialValue:'b' is valid
 PASS syntax:'<length>', initialValue:'2px' is valid
@@ -22,6 +22,7 @@ PASS syntax:'<length>', initialValue:'calc(2px*4 + 10px)' is valid
 PASS syntax:'<length>', initialValue:'7.1e-4cm' is valid
 PASS syntax:'<length>', initialValue:'calc(7in - 12px)' is valid
 PASS syntax:'<length>+', initialValue:'2px 7px calc(8px)' is valid
+PASS syntax:'<length>#', initialValue:'2px, 7px, calc(8px)' is valid
 PASS syntax:'<percentage>', initialValue:'-9.3e3%' is valid
 PASS syntax:'<length-percentage>', initialValue:'-54%' is valid
 PASS syntax:'<length-percentage>', initialValue:'0' is valid
@@ -117,6 +118,8 @@ PASS syntax:'<length>', initialValue:'calc(4px + 3em)' is invalid
 PASS syntax:'<length>', initialValue:'calc(4px + calc(8 * 2em))' is invalid
 PASS syntax:'<length>+', initialValue:'calc(2ex + 16px)' is invalid
 PASS syntax:'<length>+', initialValue:'10px calc(20px + 4rem)' is invalid
+PASS syntax:'<length>+', initialValue:'' is invalid
+PASS syntax:'<length>#', initialValue:'' is invalid
 PASS syntax:'<percentage> | <length>+', initialValue:'calc(100vh - 10px) 30px' is invalid
 PASS syntax:'<length>', initialValue:'10px;' is invalid
 PASS syntax:'<length-percentage>', initialValue:'calc(2px + 10% + 7ex)' is invalid

third_party/WebKit/LayoutTests/external/wpt/css/css-properties-values-api/register-property-syntax-parsing.html

@@ -46,6 +46,7 @@ assert_valid("<length>", "calc(2px*4 + 10px)");
 assert_valid("<length>", "7.1e-4cm");
 assert_valid("<length>", "calc(7in - 12px)");
 assert_valid("<length>+", "2px 7px calc(8px)");
+assert_valid("<length>#", "2px, 7px, calc(8px)");
 assert_valid("<percentage>", "-9.3e3%");
 assert_valid("<length-percentage>", "-54%");
 assert_valid("<length-percentage>", "0");
@@ -151,6 +152,8 @@ assert_invalid("<length>", "calc(4px + 3em)");
 assert_invalid("<length>", "calc(4px + calc(8 * 2em))");
 assert_invalid("<length>+", "calc(2ex + 16px)");
 assert_invalid("<length>+", "10px calc(20px + 4rem)");
+assert_invalid("<length>+", "");
+assert_invalid("<length>#", "");
 assert_invalid("<percentage> | <length>+", "calc(100vh - 10px) 30px");
 assert_invalid("<length>", "10px;");
 assert_invalid("<length-percentage>", "calc(2px + 10% + 7ex)");

third_party/blink/renderer/core/css/css_syntax_descriptor.cc

@@ -210,7 +210,7 @@ const CSSValue* ConsumeSyntaxComponent(const CSSSyntaxComponent& syntax,
         return nullptr;
       list->Append(*value);
     }
-    return list;
+    return list->length() ? list : nullptr;
   }
   if (syntax.GetRepeat() == CSSSyntaxRepeat::kCommaSeparated) {
     CSSValueList* list = CSSValueList::CreateCommaSeparated();
@@ -220,7 +220,7 @@ const CSSValue* ConsumeSyntaxComponent(const CSSSyntaxComponent& syntax,
         return nullptr;
       list->Append(*value);
     } while (CSSPropertyParserHelpers::ConsumeCommaIncludingWhitespace(range));
-    return list;
+    return list->length() ? list : nullptr;
   }
   const CSSValue* result = ConsumeSingleType(syntax, range, context);
   if (!range.AtEnd())