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

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

Index: third_party/WebKit/Source/core/layout/FloatingObjects.cpp
diff --git a/third_party/WebKit/Source/core/layout/FloatingObjects.cpp b/third_party/WebKit/Source/core/layout/FloatingObjects.cpp
index fe47a39ebf3370113da807baf3b59eb5c40cff3e..eff3aae9290e1e506abc86def572d67ae95ae4c9 100644
--- a/third_party/WebKit/Source/core/layout/FloatingObjects.cpp
+++ b/third_party/WebKit/Source/core/layout/FloatingObjects.cpp
@@ -27,6 +27,8 @@
 #include "core/layout/LayoutBox.h"
 #include "core/layout/LayoutView.h"
 #include "core/layout/shapes/ShapeOutsideInfo.h"
+#include "core/paint/PaintLayer.h"
+#include "platform/RuntimeEnabledFeatures.h"
 
 #include <algorithm>
 
@@ -66,7 +68,6 @@ FloatingObject::FloatingObject(LayoutBox* layoutObject, Type type, const LayoutR
     , m_originatingLine(nullptr)
     , m_frameRect(frameRect)
     , m_type(type)
-    , m_shouldPaint(shouldPaint)
     , m_isDescendant(isDescendant)
     , m_isPlaced(true)
     , m_isLowestNonOverhangingFloatInChild(isLowestNonOverhangingFloatInChild)
@@ -74,17 +75,36 @@ FloatingObject::FloatingObject(LayoutBox* layoutObject, Type type, const LayoutR
     , m_isInPlacedTree(false)
 #endif
 {
+    m_shouldPaint = shouldPaint || shouldPaintForCompositedLayoutPart();
+}
+
+bool FloatingObject::shouldPaintForCompositedLayoutPart()
+{
+    // HACK: only non-self-painting floats should paint. However, due to the fundamental compositing bug, some LayoutPart objects
+    // may become self-painting due to being composited. This leads to a chicken-egg issue because layout may not depend on compositing.
+    // If this is the case, set shouldPaint() to true even if the layer is technically self-painting. This lets the float which contains
+    // a LayoutPart start painting as soon as it stops being composited, without having to re-layout the float.
+    // This hack can be removed after SPv2.
+    return m_layoutObject->layer() && m_layoutObject->layer()->isSelfPaintingOnlyBecauseIsCompositedPart() && !RuntimeEnabledFeatures::slimmingPaintV2Enabled();
 }
 
 PassOwnPtr<FloatingObject> FloatingObject::create(LayoutBox* layoutObject)
 {
     OwnPtr<FloatingObject> newObj = adoptPtr(new FloatingObject(layoutObject));
-    newObj->setShouldPaint(!layoutObject->hasSelfPaintingLayer()); // If a layer exists, the float will paint itself. Otherwise someone else will.
+
+    // If a layer exists, the float will paint itself. Otherwise someone else will.
+    newObj->setShouldPaint(!layoutObject->hasSelfPaintingLayer() || newObj->shouldPaintForCompositedLayoutPart());
+
     newObj->setIsDescendant(true);
 
     return newObj;
 }
 
+bool FloatingObject::shouldPaint() const
+{
+    return m_shouldPaint && !m_layoutObject->hasSelfPaintingLayer();
+}
+
 PassOwnPtr<FloatingObject> FloatingObject::copyToNewContainer(LayoutSize offset, bool shouldPaint, bool isDescendant) const
 {
     return adoptPtr(new FloatingObject(layoutObject(), getType(), LayoutRect(frameRect().location() - offset, frameRect().size()), shouldPaint, isDescendant, isLowestNonOverhangingFloatInChild()));