Improved parse error handling for CSSMQ.

LayoutTests/css3/filters/custom-with-at-rule-syntax/parsing-at-rule-valid-expected.txt

Index: LayoutTests/css3/filters/custom-with-at-rule-syntax/parsing-at-rule-valid-expected.txt
diff --git a/LayoutTests/css3/filters/custom-with-at-rule-syntax/parsing-at-rule-valid-expected.txt b/LayoutTests/css3/filters/custom-with-at-rule-syntax/parsing-at-rule-valid-expected.txt
index 8d1838d15512ad989e9a0afb8f0d6ffc6443c0ee..338fb6ad49b3a9605e3f3cbaf57ed8597d621701 100644
--- a/LayoutTests/css3/filters/custom-with-at-rule-syntax/parsing-at-rule-valid-expected.txt
+++ b/LayoutTests/css3/filters/custom-with-at-rule-syntax/parsing-at-rule-valid-expected.txt
@@ -46,6 +46,15 @@ PASS declaration.getPropertyValue('width') is "100px"
 PASS declaration.getPropertyValue('height') is "100px"
 PASS declaration.length is 2
 
+Empty rule, missing closing brace.
+@-webkit-filter my-filter {
+PASS cssRule.cssText is "@-webkit-filter my-filter { }"
+PASS cssRule.type is CSSRule.WEBKIT_FILTER_RULE
+PASS cssRule instanceof WebKitCSSFilterRule is true
+PASS cssRule.constructor === WebKitCSSFilterRule is true
+PASS cssRule.__proto__ === WebKitCSSFilterRule.prototype is true
+PASS declaration.length is 0
+
 ========================================
 Nested filter at-rule tests.
 ========================================