Adapt and reland old position sticky implementation

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 f379507c3846f712a6aefd0b651ce85292fcf380..e796985bd8a421d4a158d69a5e6653d39ef4927e 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.h
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.h
@@ -222,6 +222,8 @@ public:
     // Allows updates of layer content without invalidating paint.
     void contentChanged(ContentChangeType);
 
+    void updateLayerPosition();
+
     void updateLayerPositionsAfterLayout();
     void updateLayerPositionsAfterOverflowScroll(const DoubleSize& scrollDelta);
 
@@ -533,7 +535,13 @@ public:
     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; }
@@ -636,9 +644,6 @@ private:
 
     void dirtyAncestorChainHasSelfPaintingLayerDescendantStatus();
 
-    // Returns true if the position changed.
-    bool updateLayerPosition();
-
     void updateLayerPositionRecursive();
     void updateLayerPositionsAfterScrollRecursive(const DoubleSize& scrollDelta, bool paintInvalidationContainerWasScrolled);