className should be allowed to be a whitespace-only string

third_party/WebKit/Source/core/dom/Element.cpp

Index: third_party/WebKit/Source/core/dom/Element.cpp
diff --git a/third_party/WebKit/Source/core/dom/Element.cpp b/third_party/WebKit/Source/core/dom/Element.cpp
index 9034a842ff08eed765667e4d3dfa4a467b18e33b..f41b53de90b5fcbfbfc99439d77cedff3d3aa58e 100644
--- a/third_party/WebKit/Source/core/dom/Element.cpp
+++ b/third_party/WebKit/Source/core/dom/Element.cpp
@@ -1229,7 +1229,7 @@ inline void Element::attributeChangedFromParserOrByCloning(const QualifiedName&
 }
 
 template <typename CharacterType>
-static inline bool classStringHasClassName(const CharacterType* characters, unsigned length)
+static inline ClassStringContent classStringHasClassName(const CharacterType* characters, unsigned length)
 {
     ASSERT(length > 0);
 
@@ -1240,15 +1240,20 @@ static inline bool classStringHasClassName(const CharacterType* characters, unsi
         ++i;
     } while (i < length);
 
-    return i < length;
+    if (i == length && length == 1)
+        return Empty;
+    if (i == length && length > 1)
+        return WhiteSpaceOnly;
+
+    return HasClasses;
 }
 
-static inline bool classStringHasClassName(const AtomicString& newClassString)
+static inline ClassStringContent classStringHasClassName(const AtomicString& newClassString)
 {
     unsigned length = newClassString.length();
 
     if (!length)
-        return false;
+        return Empty;
 
     if (newClassString.is8Bit())
         return classStringHasClassName(newClassString.characters8(), length);
@@ -1261,8 +1266,9 @@ void Element::classAttributeChanged(const AtomicString& newClassString)
     bool testShouldInvalidateStyle = inActiveDocument() && styleResolver && styleChangeType() < SubtreeStyleChange;
 
     ASSERT(elementData());
-    if (classStringHasClassName(newClassString)) {
-        const bool shouldFoldCase = document().inQuirksMode();
+    ClassStringContent classStringContentType = classStringHasClassName(newClassString);
+    const bool shouldFoldCase = document().inQuirksMode();
+    if (classStringContentType == HasClasses) {
         const SpaceSplitString oldClasses = elementData()->classNames();
         elementData()->setClass(newClassString, shouldFoldCase);
         const SpaceSplitString& newClasses = elementData()->classNames();
@@ -1272,7 +1278,10 @@ void Element::classAttributeChanged(const AtomicString& newClassString)
         const SpaceSplitString& oldClasses = elementData()->classNames();
         if (testShouldInvalidateStyle)
             document().styleEngine().classChangedForElement(oldClasses, *this);
-        elementData()->clearClass();
+        if (classStringContentType == WhiteSpaceOnly)
+            elementData()->setClass(newClassString, shouldFoldCase);
+        else
+            elementData()->clearClass();
     }
 
     if (hasRareData())
@@ -1297,7 +1306,8 @@ bool Element::shouldInvalidateDistributionWhenAttributeChanged(ElementShadow* el
 
     if (name == HTMLNames::classAttr) {
         const AtomicString& newClassString = newValue;
-        if (classStringHasClassName(newClassString)) {
+
+        if (classStringHasClassName(newClassString) == HasClasses) {
             const SpaceSplitString& oldClasses = elementData()->classNames();
             const SpaceSplitString newClasses(newClassString, document().inQuirksMode() ? SpaceSplitString::ShouldFoldCase : SpaceSplitString::ShouldNotFoldCase);
             if (featureSet.checkSelectorsForClassChange(oldClasses, newClasses))