Cherry-pick 5590366. rdar://123641381

    scanAttributeName doesn't need to check for "is" content attribute
    https://bugs.webkit.org/show_bug.cgi?id=270066

    Reviewed by Chris Dumez and Yusuke Suzuki.

    Since we don't support "is" content attribute, we don't need to check for its presence.

    * Source/WebCore/html/parser/HTMLDocumentParserFastPath.cpp:
    (WebCore::HTMLFastPathParser::scanAttributeName):

    Canonical link: https://commits.webkit.org/275331@main

Canonical link: https://commits.webkit.org/272448.645@safari-7618-branch

Source/WebCore/html/parser/HTMLDocumentParserFastPath.cpp

@@ -585,8 +585,6 @@ class HTMLFastPathParser {
             // fails. For example, an image's onload event.
             return nullQName();
         }
-        if (attributeName.size() == 2 && compareCharacters(attributeName.data(), 'i', 's'))
-            return nullQName();
         return HTMLNameCache::makeAttributeQualifiedName(attributeName);
     }