Check subtree paint invalidation when overflow clip status changes

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 378 matching lines @@
 {
     ASSERT(!needsLayout());
 
     PaintInvalidationState newPaintInvalidationState(paintInvalidationState, *this);
     if (!shouldCheckForPaintInvalidation(newPaintInvalidationState))
         return;
 
     LayoutRect previousPaintInvalidationRect = this->previousPaintInvalidationRect();
     LayoutPoint previousPosition = previousPositionFromPaintInvalidationBacking();
     PaintInvalidationReason reason = invalidatePaintIfNeeded(newPaintInvalidationState);
-    clearPaintInvalidationFlags(newPaintInvalidationState);
 
     if (previousPosition != previousPositionFromPaintInvalidationBacking())
         newPaintInvalidationState.setForceSubtreeInvalidationCheckingWithinContainer();
 
     // TODO(wangxianzhu): Combine this function into LayoutObject::invalidateTreeIfNeeded() when removing the following workarounds.
 
     // TODO(wangxianzhu): This is a workaround for crbug.com/533277. Will remove when we enable paint offset caching.
     if (reason != PaintInvalidationNone && hasPercentageTransform(styleRef()))
         newPaintInvalidationState.setForceSubtreeInvalidationCheckingWithinContainer();
 
     // TODO(wangxianzhu): This is a workaround for crbug.com/490725. We don't have enough saved information to do accurate check
     // of clipping change. Will remove when we remove rect-based paint invalidation.
     if (!RuntimeEnabledFeatures::slimmingPaintV2Enabled()
         && previousPaintInvalidationRect != this->previousPaintInvalidationRect()
         && !usesCompositedScrolling()
         && hasOverflowClip())
         newPaintInvalidationState.setForceSubtreeInvalidationRectUpdateWithinContainer();
 
     newPaintInvalidationState.updateForChildren(reason);
+    clearPaintInvalidationFlags(newPaintInvalidationState);

[chrishtr, 2016/05/23 20:10:32]

What does this have to do with the fix here?

[Xianzhu, 2016/05/23 21:35:49]

Now we check m_currentObject.mayNeedPaintInvalidationSubtree() in
PaintInvalidaitonState::updateForChildren(), so we must clear the paint
invalidation flags  after updateForChildren().

     invalidatePaintOfSubtreesIfNeeded(newPaintInvalidationState);
 }
 
 void LayoutBoxModelObject::setBackingNeedsPaintInvalidationInRect(const LayoutRect& r, PaintInvalidationReason invalidationReason, const LayoutObject& object) const
 {
     // TODO(wangxianzhu): Enable the following assert after paint invalidation for spv2 is ready.
     // ASSERT(!RuntimeEnabledFeatures::slimmingPaintV2Enabled());
 
     // https://bugs.webkit.org/show_bug.cgi?id=61159 describes an unreproducible crash here,
     // so assert but check that the layer is composited.
@@ skipping 687 matching lines @@
     if (rootElementStyle->hasBackground())
         return false;
 
     if (node() != document().firstBodyElement())
         return false;
 
     return true;
 }
 
 } // namespace blink