Adapt and reland old position sticky implementation

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

 /*
  * Copyright (C) 2003, 2009, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Intel Corporation. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
@@ skipping 201 matching lines @@
     LayoutRect rect() const { return LayoutRect(location(), LayoutSize(size())); }
 
     bool isRootLayer() const { return m_isRootLayer; }
 
     PaintLayerCompositor* compositor() const;
 
     // Notification from the layoutObject that its content changed (e.g. current frame of image changed).
     // Allows updates of layer content without invalidating paint.
     void contentChanged(ContentChangeType);
 
+    // Returns true if the position changed.
+    bool updateLayerPosition();

[chrishtr, 2015/12/11 02:06:12]

It appears no one cares about the return value of this method, change to void.

[flackr, 2016/01/19 15:40:48]

Done.

+
     void updateLayerPositionsAfterLayout();
     void updateLayerPositionsAfterOverflowScroll(const DoubleSize& scrollDelta);
 
     PaintLayer* enclosingPaginationLayer() const { return m_enclosingPaginationLayer; }
 
     void updateTransformationMatrix();
     PaintLayer* renderingContextRoot();
 
     const LayoutSize& offsetForInFlowPosition() const { return m_offsetForInFlowPosition; }
 
@@ skipping 301 matching lines @@
         // While we're updating the compositing inputs, these values may differ.
         // We should never be asking for this value when that is the case.
         ASSERT(m_needsDescendantDependentCompositingInputsUpdate == m_needsAncestorDependentCompositingInputsUpdate);
         return m_needsDescendantDependentCompositingInputsUpdate;
     }
 
     void updateAncestorDependentCompositingInputs(const AncestorDependentCompositingInputs&);
     void updateDescendantDependentCompositingInputs(const DescendantDependentCompositingInputs&);
     void didUpdateCompositingInputs();
 
-    const AncestorDependentCompositingInputs& ancestorDependentCompositingInputs() const { ASSERT(!m_needsAncestorDependentCompositingInputsUpdate); return m_ancestorDependentCompositingInputs; }
+    const AncestorDependentCompositingInputs& ancestorDependentCompositingInputs() const
+    {
+        // TODO(flackr): When we process scroll updates after compositing updates we won't be querying ancestor
+        // dependent compositing inputs while they're still needed: http://crbug.com/420741.
+        ASSERT(isAllowedToQueryCompositingState() || !m_needsAncestorDependentCompositingInputsUpdate);
+        return m_ancestorDependentCompositingInputs;
+    }
     const DescendantDependentCompositingInputs& descendantDependentCompositingInputs() const { ASSERT(!m_needsDescendantDependentCompositingInputsUpdate); return m_descendantDependentCompositingInputs; }
 
     IntRect clippedAbsoluteBoundingBox() const { return ancestorDependentCompositingInputs().clippedAbsoluteBoundingBox; }
     const PaintLayer* opacityAncestor() const { return ancestorDependentCompositingInputs().opacityAncestor; }
     const PaintLayer* transformAncestor() const { return ancestorDependentCompositingInputs().transformAncestor; }
     const PaintLayer* filterAncestor() const { return ancestorDependentCompositingInputs().filterAncestor; }
     const LayoutObject* clippingContainer() const { return ancestorDependentCompositingInputs().clippingContainer; }
     const PaintLayer* ancestorScrollingLayer() const { return ancestorDependentCompositingInputs().ancestorScrollingLayer; }
     const PaintLayer* nearestFixedPositionLayer() const { return ancestorDependentCompositingInputs().nearestFixedPositionLayer; }
     PaintLayer* scrollParent() const { return const_cast<PaintLayer*>(ancestorDependentCompositingInputs().scrollParent); }
@@ skipping 67 matching lines @@
     PaintTiming* paintTiming();
 
 private:
     // Bounding box in the coordinates of this layer.
     LayoutRect logicalBoundingBox() const;
 
     bool hasOverflowControls() const;
 
     void dirtyAncestorChainHasSelfPaintingLayerDescendantStatus();
 
-    // Returns true if the position changed.
-    bool updateLayerPosition();
-
     void updateLayerPositionRecursive();
     void updateLayerPositionsAfterScrollRecursive(const DoubleSize& scrollDelta, bool paintInvalidationContainerWasScrolled);
 
     void setNextSibling(PaintLayer* next) { m_next = next; }
     void setPreviousSibling(PaintLayer* prev) { m_previous = prev; }
     void setFirstChild(PaintLayer* first) { m_first = first; }
     void setLastChild(PaintLayer* last) { m_last = last; }
 
     void updateHasSelfPaintingLayerDescendant() const;
     PaintLayer* hitTestLayer(PaintLayer* rootLayer, PaintLayer* containerLayer, HitTestResult&,
@@ skipping 169 matching lines @@
 
 } // namespace blink
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showLayerTree(const blink::PaintLayer*);
 void showLayerTree(const blink::LayoutObject*);
 #endif
 
 #endif // Layer_h