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 b190197cf90abb94029d6366dba38807390cc17e..6dd2881d7e8f49bc3175c9d54507933e1f9f367b 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     // FIXME: Many people call this function while it has out-of-date information.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;
+
     void setLayerType(PaintLayerType layerType) { m_layerType = layerType; ASSERT(static_cast<PaintLayerType>(m_layerType) == layerType); }
 
     bool isTransparent() const { return layoutObject()->isTransparent() || layoutObject()->style()->hasBlendMode() || layoutObject()->hasMask(); }
@@ -786,6 +790,8 @@ private:
         m_needsPaintPhaseDescendantBlockBackgrounds |= layer.m_needsPaintPhaseDescendantBlockBackgrounds;
     }
 
+    bool isSelfPaintingLayerForIntrinsicOrScrollingReasons() const;
+
     unsigned m_layerType : 2; // PaintLayerType
 
     // Self-painting layer is an optimization where we avoid the heavy Layer painting