Improved parse error handling for CSSMQ.

LayoutTests/css3/filters/custom-with-at-rule-syntax/script-tests/parsing-at-rule-valid.js

 // Requires custom-filter-parsing-common.js.
 
 description("Test at-rule parsing for @-webkit-filter.");
 
 // These have to be global for the test helpers to see them.
 var cssRule, declaration;
 
 function testFilterAtRule(description, rule, expectedValue, expectedProperties)
 {
     debug("\n" + description + "\n" + rule);
@@ skipping 52 matching lines @@
 testFilterAtRule("Empty rule, separated by multiple spaces.",
     "   @-webkit-filter   my-filter   {   }   ",
     "@-webkit-filter my-filter { }");
 testFilterAtRule("Empty rule, no extra whitespace.",
     "@-webkit-filter my-filter{}",
     "@-webkit-filter my-filter { }");
 testFilterAtRule("Rule with arbitrary properties.",
     "@-webkit-filter my-filter { width: 100px; height: 100px; }", 
     "@-webkit-filter my-filter { width: 100px; height: 100px; }",
     {width: "100px", height: "100px"});
+testFilterAtRule("Empty rule, missing closing brace.",
+    "@-webkit-filter my-filter {",
+    "@-webkit-filter my-filter { }");
 
 heading("Nested filter at-rule tests.");
 testNestedRules("Nested rule.",
     "@-webkit-filter parent-filter { @-webkit-filter child-filter { } }", 
     {
         cssText: "@-webkit-filter parent-filter { }",
         ruleType: CSSRule.WEBKIT_FILTER_RULE,
         constructorName: "WebKitCSSFilterRule"
     });
 testNestedRules("Twice nested rule.",
@@ skipping 15 matching lines @@
     {
         cssText: "@media screen { \n  @-webkit-filter child-filter { }\n}",
         ruleType: CSSRule.MEDIA_RULE,
         constructorName: "CSSMediaRule",
     },
     {
         cssText: "@-webkit-filter child-filter { }",
         ruleType: CSSRule.WEBKIT_FILTER_RULE,
         constructorName: "WebKitCSSFilterRule",
     });