[@property] Serialize property name as an identifier

The serialization must follow the "serialize an identifier" algorithm,
otherwise characters like U+0009 CHARACTER TABULATION will not be
escaped correctly.

Bug: 973830
Change-Id: I2dc943a74900adaf147e1615070c152a78cb5767
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2238117Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Commit-Queue: Anders Hartvoll Ruud <andruud@chromium.org>
Cr-Commit-Position: refs/heads/master@{#777302}

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

@@ -5,6 +5,7 @@
 #include "third_party/blink/renderer/core/css/css_property_rule.h"
 
 #include "third_party/blink/renderer/core/css/css_identifier_value.h"
+#include "third_party/blink/renderer/core/css/css_markup.h"
 #include "third_party/blink/renderer/core/css/css_property_value_set.h"
 #include "third_party/blink/renderer/core/css/css_string_value.h"
 #include "third_party/blink/renderer/core/css/style_rule.h"
@@ -24,7 +25,7 @@ String CSSPropertyRule::cssText() const {
   // https://drafts.css-houdini.org/css-properties-values-api-1/#serialize-a-csspropertyrule
   StringBuilder builder;
   builder.Append("@property ");
-  builder.Append(property_rule_->GetName());
+  SerializeIdentifier(property_rule_->GetName(), builder);
   builder.Append(" { ");
   if (const CSSValue* syntax = property_rule_->GetSyntax()) {
     DCHECK(syntax->IsStringValue());

third_party/blink/web_tests/external/wpt/css/css-properties-values-api/at-property-cssom.html

@@ -51,6 +51,8 @@
   @property --initial-value-only {
     initial-value: red;
   }
+  /* U+0009 CHARACTER TABULATION */
+  @property --tab\9 tab {  }
 </style>
 <script>
 
@@ -119,6 +121,7 @@ test_css_text('--no-initial-value', '@property --no-initial-value { syntax: "<co
 test_css_text('--syntax-only', '@property --syntax-only { syntax: "<color> | none"; }');
 test_css_text('--inherits-only', '@property --inherits-only { inherits: true; }');
 test_css_text('--initial-value-only', '@property --initial-value-only { initial-value: red; }');
+test_css_text('--tab\ttab', '@property --tab\\9 tab { }');
 
 // CSSRule.type