Add support for case-insensitive attribute value selectors

Source/core/css/SelectorChecker.cpp

Index: Source/core/css/SelectorChecker.cpp
diff --git a/Source/core/css/SelectorChecker.cpp b/Source/core/css/SelectorChecker.cpp
index 3e205e96ac78575f4084fffac61a2f1747ebd2be..2f71c6982fc16f8668fb346c96a273313722559c 100644
--- a/Source/core/css/SelectorChecker.cpp
+++ b/Source/core/css/SelectorChecker.cpp
@@ -498,7 +498,8 @@ static bool anyAttributeMatches(Element& element, CSSSelector::Match match, cons
     if (!element.hasAttributesWithoutUpdate())
         return false;
 
-    const AtomicString& selectorValue =  selector.value();
+    const AtomicString& selectorValue = selector.value();
+    bool caseInsensitive = selector.attributeFlags() & CSSSelector::CaseInsensitive;
 
     AttributeIteratorAccessor attributes = element.attributesIterator();
     AttributeConstIterator end = attributes.end();
@@ -508,9 +509,12 @@ static bool anyAttributeMatches(Element& element, CSSSelector::Match match, cons
         if (!attributeItem.matches(selectorAttr))
             continue;
 
-        if (attributeValueMatches(attributeItem, match, selectorValue, true))
+        if (attributeValueMatches(attributeItem, match, selectorValue, !caseInsensitive))
             return true;
 
+        if (caseInsensitive)
+            continue;
+
         // Case sensitivity for attribute matching is looser than hasAttribute or
         // Element::shouldIgnoreAttributeCase() for now. Unclear if that's correct.
         bool caseSensitive = !element.document().isHTMLDocument() || HTMLDocument::isCaseSensitiveAttribute(selectorAttr);

[Timothy Loh, 2014/07/22 08:51:02]

This is super confusing (we have a caseSensitive and a caseInsensitive variable
in the same scope)! Can we rename things and tweak comments to aid comprehension
here?

[fs, 2014/07/22 11:06:17]

I suppose we could make the new (currently |caseInsensitive|)
|selectorCaseInsensitive| or somesuch. Maybe |matchAttrCaseSensitive(ly)| for
the current |caseSensitive|? Naming is hard though, so I'll gladly take
suggestions...

What kind of comment tweaks were you envisioning?

[Timothy Loh, 2014/07/22 11:50:26]

If I'm reading crbug.com/327060 right, the existing |caseSensitive| branch is
legacy behaviour that we want to remove and this patch will allow us to tweak
our UA stylesheets to not hit this case. So perhaps keep |caseInsensitive| as
is, but change |caseSensitive| into |legacyCaseInsensitive|.

I would write a comment like "Legacy behavior is to treat values for some
attributes as case insensitive regardless of whether the case insensitive flag
is set" but feel free to write what makes the most sense to you; the existing
bug link here is probably the most useful part.

[fs, 2014/07/22 14:09:04]

Thank you for elaborating. I've updated to something like the above.

[Timothy Loh, 2014/07/23 01:46:50]

I think |legacyCaseInsensitive| (instead of |legacyCaseSensitive|) makes this
slightly easier to understand