DevTools: recognize CSSIdentifiers that start with double hyphen

third_party/WebKit/Source/devtools/front_end/components/DOMPresentationUtils.js

Index: third_party/WebKit/Source/devtools/front_end/components/DOMPresentationUtils.js
diff --git a/third_party/WebKit/Source/devtools/front_end/components/DOMPresentationUtils.js b/third_party/WebKit/Source/devtools/front_end/components/DOMPresentationUtils.js
index 960c9e1bd90c07cb65ecf57d79e7741bb3d68562..679710f759ba437f82a8e5964e9e126408b7275c 100644
--- a/third_party/WebKit/Source/devtools/front_end/components/DOMPresentationUtils.js
+++ b/third_party/WebKit/Source/devtools/front_end/components/DOMPresentationUtils.js
@@ -415,7 +415,8 @@ Components.DOMPresentationUtils._cssPathStep = function(node, optimized, isTarge
    * @return {boolean}
    */
   function isCSSIdentifier(value) {
-    return /^-?[a-zA-Z_][a-zA-Z0-9_-]*$/.test(value);
+    // Double hyphen prefixes are not allowed by specification, but many sites use it.
+    return /^-{0,2}[a-zA-Z_][a-zA-Z0-9_-]*$/.test(value);
   }
 
   var prefixedOwnClassNamesArray = prefixedElementClassNames(node);