Implement all shorthand property.

Source/core/css/CSSComputedStyleDeclaration.cpp

Index: Source/core/css/CSSComputedStyleDeclaration.cpp
diff --git a/Source/core/css/CSSComputedStyleDeclaration.cpp b/Source/core/css/CSSComputedStyleDeclaration.cpp
index 67e2a34c66c8ec3505ceb574d0129edd91fb2c0c..543148afe1b162a5ca872061a6e320cb23f07ff5 100644
--- a/Source/core/css/CSSComputedStyleDeclaration.cpp
+++ b/Source/core/css/CSSComputedStyleDeclaration.cpp
@@ -2853,6 +2853,23 @@ PassRefPtrWillBeRawPtr<CSSValue> CSSComputedStyleDeclaration::getPropertyCSSValu
         case CSSPropertyPaintOrder:
         case CSSPropertyWritingMode:
             return getSVGPropertyCSSValue(propertyID, DoNotUpdateLayout);
+
+        case CSSPropertyAll:
+        {
+            // FIXME: need to support "unset".
+            bool isInitial = true;
+            bool isInherit = true;
+            for (unsigned i = 0; i < allShorthand().length() && (isInitial || isInherit); ++i) {
+                RefPtrWillBeRawPtr<CSSValue> value = getPropertyCSSValue(allShorthand().properties()[i], DoNotUpdateLayout);
+                isInitial = isInitial && value->isInitialValue();
+                isInherit = isInherit && value->isInheritedValue();
+            }
+            if (isInitial)
+                return cssValuePool().createExplicitInitialValue();
+            if (isInherit)
+                return cssValuePool().createInheritedValue();
+            return nullptr;
+        }
     }
 
     logUnimplementedPropertyID(propertyID);