Remove unnecessary checks in PaintLayer::backgroundIsKnownToBeOpaqueInRect

third_party/WebKit/Source/core/paint/PaintLayer.cpp

Index: third_party/WebKit/Source/core/paint/PaintLayer.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayer.cpp b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
index 37a94ac80e0939e43eb374798ff3684fdb5e86ef..454528f98a933b67f543818b5dad9c09d1735297 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
@@ -2397,9 +2397,6 @@ bool PaintLayer::paintsWithTransform(GlobalPaintFlags globalPaintFlags) const
 
 bool PaintLayer::backgroundIsKnownToBeOpaqueInRect(const LayoutRect& localRect) const
 {
-    if (!isSelfPaintingLayer() && !hasSelfPaintingLayerDescendant())

[chrishtr, 2016/08/30 20:49:01]

childBackgroundIsKnownToBeOpaqueInRect calls backgroundIsKnownToBeOpaqueInRect
on all stacking-children
PaintLayers that paint into the same backing. They don't have to be
self-painting, right?

[Stephen Chennney, 2016/08/30 20:58:51]

Right, in fact we only want the ones that are not self painting, because self
painters contribute to a different backing. That check already exists in
childBackgroundIsKnownToBeOpaqueInRect, in the form of
childLayer->isPaintInvalidationContainer()

[chrishtr, 2016/08/30 21:15:39]

No. self-painting is not the same thing as independently composited.
self-painting means something
sort of like stacking context.

-        return false;
-
     if (paintsWithTransparency(GlobalPaintNormalPhase))
         return false;
 
@@ -2415,14 +2412,12 @@ bool PaintLayer::backgroundIsKnownToBeOpaqueInRect(const LayoutRect& localRect)
     if (paintsWithTransform(GlobalPaintNormalPhase))
         return false;
 
-    // FIXME: Remove this check.
     // This function should not be called when layer-lists are dirty.
-    // It is somehow getting triggered during style update.
-    if (m_stackingNode->zOrderListsDirty())
-        return false;
+    DCHECK(!m_stackingNode->zOrderListsDirty());
 
     // FIXME: We currently only check the immediate layoutObject,
-    // which will miss many cases.
+    // which will miss many cases where additional layout objects paint
+    // into this layer.
     if (layoutObject()->backgroundIsKnownToBeOpaqueInRect(localRect))
         return true;