Conic gradient parsing support

third_party/WebKit/Source/core/css/CSSValueKeywords.json5

 {
   // The mode argument is used to limit the keyword to be used only for certain
   // CSSParserModes. Values that have the prefix -internal- are only allowed by
   // CSSParserModes listed in allowInternalPropertyAndValue()
 
   parameters: {
     mode: {},
   },
 
   //
@@ skipping 998 matching lines @@
 
     // all
     // initial
     // inherit
     "revert",
     "unset",
 
     // background-image, etc.
     "linear-gradient",
     "radial-gradient",
+    "conic-gradient",
     "repeating-linear-gradient",
     "repeating-radial-gradient",
+    "repeating-conic-gradient",
     "paint",
     "-webkit-cross-fade",
     "-webkit-gradient",
     "-webkit-linear-gradient",
     "-webkit-radial-gradient",
     "-webkit-repeating-linear-gradient",
     "-webkit-repeating-radial-gradient",
     "-webkit-image-set",
 
     // deprecated gradients
@@ skipping 93 matching lines @@
     // shape
     // rect
     // round
 
     // color-gamut
     // srgb
     "p3",
     "rec2020",
   ],
 }