Fix border radius on composited children.

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 5095e4701536c26aa63e463e489a22e4ab56ee68..87bf4ec0b3888d1a889d1904b4843c73008ea1de 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBox.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
@@ -2277,6 +2277,13 @@ bool LayoutBox::paintedOutputOfObjectHasNoEffectRegardlessOfSize() const {
       return false;
   }
 
+  // If the box paints into its own backing, we can assume that it's painting
+  // may have some effect. For example, honoring the border-radius clip on
+  // a composited child paints into a mask for an otherwise non-painting
+  // element, because children of that element will require the mask.
+  if (hasLayer() && layer()->compositingState() == PaintsIntoOwnBacking)

[Stephen Chennney, 2017/01/04 19:22:46]

This is to avoid the assert that verifies an empty display list for objects that
return true here.

+    return false;
+
   return true;
 }