Implement 'will-change' parsing

Source/core/css/resolver/StyleBuilderCustom.cpp

Index: Source/core/css/resolver/StyleBuilderCustom.cpp
diff --git a/Source/core/css/resolver/StyleBuilderCustom.cpp b/Source/core/css/resolver/StyleBuilderCustom.cpp
index a30084fe0034412b92288c9e67c730e7b1aa52c2..d1daf005af4a31d68161da18c57e598b4bbba292 100644
--- a/Source/core/css/resolver/StyleBuilderCustom.cpp
+++ b/Source/core/css/resolver/StyleBuilderCustom.cpp
@@ -864,6 +864,43 @@ void StyleBuilderFunctions::applyValueCSSPropertyTextUnderlinePosition(StyleReso
     state.style()->setTextUnderlinePosition(static_cast<TextUnderlinePosition>(t));
 }
 
+void StyleBuilderFunctions::applyInitialCSSPropertyWillChange(StyleResolverState& state)
+{
+    state.style()->setWillChangeContents(false);
+    state.style()->setWillChangeScrollPosition(false);
+    state.style()->setWillChangeProperties(Vector<CSSPropertyID>());
+}
+
+void StyleBuilderFunctions::applyInheritCSSPropertyWillChange(StyleResolverState& state)
+{
+    state.style()->setWillChangeContents(state.parentStyle()->willChangeContents());
+    state.style()->setWillChangeScrollPosition(state.parentStyle()->willChangeScrollPosition());
+    state.style()->setWillChangeProperties(state.parentStyle()->willChangeProperties());
+}
+
+void StyleBuilderFunctions::applyValueCSSPropertyWillChange(StyleResolverState& state, CSSValue* value)
+{
+    ASSERT(value->isValueList());
+    bool willChangeContents = false;
+    bool willChangeScrollPosition = false;
+    Vector<CSSPropertyID> willChangeProperties;
+
+    for (CSSValueListIterator i(value); i.hasMore(); i.advance()) {
+        CSSPrimitiveValue* primitiveValue = toCSSPrimitiveValue(i.value());
+        if (CSSPropertyID propertyID = primitiveValue->getPropertyID())
+            willChangeProperties.append(propertyID);
+        else if (primitiveValue->getValueID() == CSSValueContents)
+            willChangeContents = true;
+        else if (primitiveValue->getValueID() == CSSValueScrollPosition)
+            willChangeScrollPosition = true;
+        else
+            ASSERT_NOT_REACHED();
+    }
+    state.style()->setWillChangeContents(willChangeContents);
+    state.style()->setWillChangeScrollPosition(willChangeScrollPosition);
+    state.style()->setWillChangeProperties(willChangeProperties);
+}
+
 // Everything below this line is from the old StyleResolver::applyProperty
 // and eventually needs to move into new StyleBuilderFunctions calls intead.
 
@@ -1944,6 +1981,7 @@ void StyleBuilder::oldApplyProperty(CSSPropertyID id, StyleResolverState& state,
     case CSSPropertyWhiteSpace:
     case CSSPropertyWidows:
     case CSSPropertyWidth:
+    case CSSPropertyWillChange:
     case CSSPropertyWordBreak:
     case CSSPropertyWordSpacing:
     case CSSPropertyWordWrap: