Paint local attachment backgrounds into composited scrolling contents layer

third_party/WebKit/Source/core/style/ComputedStyleConstants.h

Index: third_party/WebKit/Source/core/style/ComputedStyleConstants.h
diff --git a/third_party/WebKit/Source/core/style/ComputedStyleConstants.h b/third_party/WebKit/Source/core/style/ComputedStyleConstants.h
index 7b259ea7438aff334d4488e9ad4bb7be6d13d5e5..61646e5585c7fa94f3a741bd64ad68a6b3e8939b 100644
--- a/third_party/WebKit/Source/core/style/ComputedStyleConstants.h
+++ b/third_party/WebKit/Source/core/style/ComputedStyleConstants.h
@@ -180,6 +180,17 @@ enum EFillBox {
     BorderFillBox, PaddingFillBox, ContentFillBox, TextFillBox
 };
 
+inline EFillBox enclosingFillBox(EFillBox boxA, EFillBox boxB)
+{
+    if (boxA == BorderFillBox || boxB == BorderFillBox)
+        return BorderFillBox;
+    if (boxA == PaddingFillBox || boxB == PaddingFillBox)
+        return PaddingFillBox;
+    if (boxA == ContentFillBox || boxB == ContentFillBox)
+        return ContentFillBox;
+    return TextFillBox;
+}
+
 enum EFillRepeat {
     RepeatFill, NoRepeatFill, RoundFill, SpaceFill
 };