Paint local attachment backgrounds into composited scrolling contents layer

third_party/WebKit/Source/core/layout/LayoutBox.h

Index: third_party/WebKit/Source/core/layout/LayoutBox.h
diff --git a/third_party/WebKit/Source/core/layout/LayoutBox.h b/third_party/WebKit/Source/core/layout/LayoutBox.h
index 99c342b09fb7bc2f96d986827575ba24c5d1232d..8ccda48de757c2d34f20a33e131e32f190c46f15 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBox.h
+++ b/third_party/WebKit/Source/core/layout/LayoutBox.h
@@ -45,6 +45,7 @@ enum AvailableLogicalHeightType { ExcludeMarginBorderPadding, IncludeMarginBorde
 // clipping behavior. During hit testing, overlay scrollbars behave like regular
 // scrollbars and should change how hit testing is clipped.
 enum MarginDirection { BlockDirection, InlineDirection };
+enum BackgroundRectOpacity { TranslucentBackgroundRect, OpaqueBackgroundRect };

[chrishtr, 2016/08/12 17:03:00]

The meaning of these enum values is not that clear. Rename or add a comment. I
thin they mean

TranslucentBackgroundRect: consider all fill layers
OpaqueBackgroundRect: consider only opaque fill layers

 
 enum ShouldComputePreferred { ComputeActual, ComputePreferred };
 
@@ -355,8 +356,8 @@ public:
     IntSize absoluteContentBoxOffset() const;
     // The content box converted to absolute coords (taking transforms into account).
     FloatQuad absoluteContentQuad() const;
-    // The clip rect of the background.
-    LayoutRect backgroundClipRect() const;
+    // The enclosing rectangle of the background with given opacity requirement.
+    LayoutRect backgroundRect(BackgroundRectOpacity) const;
 
     // This returns the content area of the box (excluding padding and border). The only difference with contentBoxRect is that computedCSSContentBoxRect
     // does include the intrinsic padding in the content box as this is what some callers expect (like getComputedStyle).