Add a hack to set shouldPaint to true for force-composited iframes.

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

Index: third_party/WebKit/Source/core/paint/PaintLayer.h
diff --git a/third_party/WebKit/Source/core/paint/PaintLayer.h b/third_party/WebKit/Source/core/paint/PaintLayer.h
index d306fce7c649084dfa22b2336b6a6bd0ff614e4c..5eb1c325dfed98001f7f4f27ba6ee5b30c982e1f 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.h
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.h
@@ -239,6 +239,10 @@ public:
     // FIXME: Many people call this function while it has out-of-date information.
     bool isSelfPaintingLayer() const { return m_isSelfPaintingLayer; }
 
+    // PaintLayers which represent LayoutParts may become self-painting due to being composited.
+    // If this is the case, this method returns true.
+    bool isSelfPaintingOnlyBecauseIsCompositedPart() const;
+
     bool isTransparent() const { return layoutObject()->isTransparent() || layoutObject()->style()->hasBlendMode() || layoutObject()->hasMask(); }
 
     bool isReflection() const { return layoutObject()->isReplica(); }
@@ -784,6 +788,8 @@ private:
         m_needsPaintPhaseDescendantBlockBackgrounds |= layer.m_needsPaintPhaseDescendantBlockBackgrounds;
     }
 
+    bool isSelfPaintingLayerForIntrinsicOrScrollingReasons() const;
+
     // Self-painting layer is an optimization where we avoid the heavy Layer painting
     // machinery for a Layer allocated only to handle the overflow clip case.
     // FIXME(crbug.com/332791): Self-painting layer should be merged into the overflow-only concept.