Ensure that we don't allow 'none' alongside other values in content property

third_party/WebKit/LayoutTests/css-parser/content-parsing.html

Index: third_party/WebKit/LayoutTests/css-parser/content-parsing.html
diff --git a/third_party/WebKit/LayoutTests/css-parser/content-parsing.html b/third_party/WebKit/LayoutTests/css-parser/content-parsing.html
index 120e377a5776360a4480587c344fa5afaaa3065a..c6893cfedb87f498e9a2a9854218047651ef3036 100644
--- a/third_party/WebKit/LayoutTests/css-parser/content-parsing.html
+++ b/third_party/WebKit/LayoutTests/css-parser/content-parsing.html
@@ -6,6 +6,7 @@
 assert_valid_value("content", '"a"');
 assert_valid_value("content", "open-quote");
 assert_valid_value("content", "normal");
+assert_valid_value("content", "none");
 assert_valid_value("content", 'url("test.html")');
 
 assert_invalid_value("content", 'normal normal');
@@ -15,6 +16,15 @@ assert_invalid_value("content", "normal open-quote");
 assert_invalid_value("content", '"a" normal');
 assert_invalid_value("content", 'url("test.html") normal');
 assert_invalid_value("content", "'open-quote' normal");
+assert_invalid_value("content", 'normal none');
+assert_invalid_value("content", 'none normal');
+assert_invalid_value("content", 'none none');
+assert_invalid_value("content", 'none "a"');
+assert_invalid_value("content", 'none url("test.html")');
+assert_invalid_value("content", "none open-quote");
+assert_invalid_value("content", '"a" none');
+assert_invalid_value("content", 'url("test.html") none');
+assert_invalid_value("content", "open-quote none");
 assert_invalid_value("content", "not valid content");
 assert_invalid_value("content", "open-quote invalid content");
 assert_invalid_value("content", '"a" still not valid');