blink: Add backdrop-filter support

Source/core/css/ComputedStyleCSSValueMapping.cpp

Index: Source/core/css/ComputedStyleCSSValueMapping.cpp
diff --git a/Source/core/css/ComputedStyleCSSValueMapping.cpp b/Source/core/css/ComputedStyleCSSValueMapping.cpp
index c84bc0dd9a013b213141221b150ca5d90b7c29dd..0507c0a298114b9ffe06435e4839ea9ae5c82fd8 100644
--- a/Source/core/css/ComputedStyleCSSValueMapping.cpp
+++ b/Source/core/css/ComputedStyleCSSValueMapping.cpp
@@ -1238,16 +1238,16 @@ PassRefPtrWillBeRawPtr<CSSValue> ComputedStyleCSSValueMapping::valueForShadowLis
     return list.release();
 }
 
-PassRefPtrWillBeRawPtr<CSSValue> ComputedStyleCSSValueMapping::valueForFilter(const ComputedStyle& style)
+PassRefPtrWillBeRawPtr<CSSValue> ComputedStyleCSSValueMapping::valueForFilter(const ComputedStyle& style, const FilterOperations& filterOperations)
 {
-    if (style.filter().operations().isEmpty())
+    if (filterOperations.operations().isEmpty())
         return cssValuePool().createIdentifierValue(CSSValueNone);
 
     RefPtrWillBeRawPtr<CSSValueList> list = CSSValueList::createSpaceSeparated();
 
     RefPtrWillBeRawPtr<CSSFunctionValue> filterValue = nullptr;
 
-    for (const auto& operation : style.filter().operations()) {
+    for (const auto& operation : filterOperations.operations()) {
         FilterOperation* filterOperation = operation.get();
         switch (filterOperation->type()) {
         case FilterOperation::REFERENCE:
@@ -2350,7 +2350,9 @@ PassRefPtrWillBeRawPtr<CSSValue> ComputedStyleCSSValueMapping::get(CSSPropertyID
     case CSSPropertyShapeOutside:
         return valueForShape(style, style.shapeOutside());
     case CSSPropertyWebkitFilter:
-        return valueForFilter(style);
+        return valueForFilter(style, style.filter());
+    case CSSPropertyBackdropFilter:
+        return valueForFilter(style, style.backdropFilter());
     case CSSPropertyMixBlendMode:
         return cssValuePool().createValue(style.blendMode());