Paint local attachment backgrounds into composited scrolling contents layer

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

Index: third_party/WebKit/Source/core/layout/LayoutBox.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBox.cpp b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
index 246ccabb2e3a81e661dac034b68b9c451e15b57f..0cfbb374950d74f1d459ac342b00b0fed8cf98ff 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBox.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
@@ -727,6 +727,51 @@ LayoutRect LayoutBox::backgroundClipRect() const
     return LayoutRect();
 }
 
+LayoutRect LayoutBox::opaqueBackgroundClipRect() const
+{
+    EFillBox backgroundClip = TextFillBox;
+    // Find the largest opaque background clip rect.
+    // TODO(flackr): Unify with the above method.
+    if (const FillLayer* current = &(style()->backgroundLayers())) {
+        do {
+            const FillLayer* cur = current;
+            current = current->next();
+            if (cur->blendMode() != WebBlendModeNormal || cur->composite() != CompositeSourceOver)
+                continue;
+            // Check if the image or color has alpha.
+            if (const StyleImage* image = cur->image()) {
+                if (!image->knownToBeOpaque(*this))
+                    continue;
+            } else {
+                Color backgroundColor = resolveColor(CSSPropertyBackgroundColor);
+                if (backgroundColor.hasAlpha())
+                    continue;
+            }
+            EFillBox currentClip = cur->clip();
+            // Adjust clip if attachment is local.
+            if (currentClip == BorderFillBox && cur->attachment() == LocalBackgroundAttachment)
+                currentClip = PaddingFillBox;
+            // TODO(flackr): Expose and use clipMax method from FillLayer.cpp.
+            if (currentClip < backgroundClip)
+                backgroundClip = currentClip;
+        } while (current);
+    }
+    switch (backgroundClip) {
+    case BorderFillBox:
+        return borderBoxRect();
+        break;
+    case PaddingFillBox:
+        return paddingBoxRect();
+        break;
+    case ContentFillBox:
+        return contentBoxRect();
+        break;
+    default:
+        break;
+    }
+    return LayoutRect();
+}
+
 void LayoutBox::addOutlineRects(Vector<LayoutRect>& rects, const LayoutPoint& additionalOffset, IncludeBlockVisualOverflowOrNot) const
 {
     rects.append(LayoutRect(additionalOffset, size()));
@@ -1395,10 +1440,6 @@ bool LayoutBox::backgroundIsKnownToBeOpaqueInRect(const LayoutRect& localRect) c
     if (isDocumentElement() || backgroundStolenForBeingBody())
         return false;
 
-    Color backgroundColor = resolveColor(CSSPropertyBackgroundColor);
-    if (backgroundColor.hasAlpha())
-        return false;
-
     // If the element has appearance, it might be painted by theme.
     // We cannot be sure if theme paints the background opaque.
     // In this case it is safe to not assume opaqueness.
@@ -1412,10 +1453,9 @@ bool LayoutBox::backgroundIsKnownToBeOpaqueInRect(const LayoutRect& localRect) c
         return false;
     if (hasClipPath())
         return false;
-    // FIXME: The background color clip is defined by the last layer.
-    if (style()->backgroundLayers().next())
+    if (style()->hasBlendMode())
         return false;
-    return backgroundClipRect().contains(localRect);
+    return opaqueBackgroundClipRect().contains(localRect);
 }
 
 static bool isCandidateForOpaquenessTest(const LayoutBox& childBox)