Reland main thread position sticky implementation.

third_party/WebKit/Source/core/layout/compositing/CompositingInputsUpdater.cpp

Index: third_party/WebKit/Source/core/layout/compositing/CompositingInputsUpdater.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/CompositingInputsUpdater.cpp b/third_party/WebKit/Source/core/layout/compositing/CompositingInputsUpdater.cpp
index f100b65849161ef94c61cb757897a82f49bfa063..c823e20b596812da42f09521694149aecc0a71ba 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositingInputsUpdater.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositingInputsUpdater.cpp
@@ -4,7 +4,9 @@
 
 #include "core/layout/compositing/CompositingInputsUpdater.h"
 
+#include "core/frame/FrameView.h"
 #include "core/layout/LayoutBlock.h"
+#include "core/layout/LayoutView.h"
 #include "core/layout/compositing/CompositedLayerMapping.h"
 #include "core/layout/compositing/PaintLayerCompositor.h"
 #include "core/paint/PaintLayer.h"
@@ -97,6 +99,28 @@ void CompositingInputsUpdater::updateRecursive(PaintLayer* layer, UpdateType upd
     if (!layer->childNeedsCompositingInputsUpdate() && updateType != ForceUpdate)
         return;
 
+    const PaintLayer* previousOverflowLayer = layer->ancestorOverflowLayer();
+    layer->updateAncestorOverflowLayer(info.lastOverflowClipLayer);
+    if (info.lastOverflowClipLayer && layer->needsCompositingInputsUpdate() && layer->layoutObject()->style()->position() == StickyPosition) {
+        if (info.lastOverflowClipLayer != previousOverflowLayer) {
+            // Old ancestor scroller should no longer have these constraints.
+            ASSERT(!previousOverflowLayer || !previousOverflowLayer->getScrollableArea()->stickyConstraintsMap().contains(layer));
+
+            if (info.lastOverflowClipLayer->isRootLayer())
+                layer->layoutObject()->view()->frameView()->addViewportConstrainedObject(layer->layoutObject());
+            else if (previousOverflowLayer && previousOverflowLayer->isRootLayer())
+                layer->layoutObject()->view()->frameView()->removeViewportConstrainedObject(layer->layoutObject());
+        }
+        layer->layoutObject()->updateStickyPositionConstraints();
+
+        // Sticky position constraints and ancestor overflow scroller affect
+        // the sticky layer position, so we need to update it again here.
+        // TODO(flackr): This should be refactored in the future to be clearer
+        // (i.e. update layer position and ancestor inputs updates in the
+        // same walk)
+        layer->updateLayerPosition();
+    }
+
     m_geometryMap.pushMappingsToAncestor(layer, layer->parent());
 
     if (layer->hasCompositedLayerMapping())
@@ -163,6 +187,9 @@ void CompositingInputsUpdater::updateRecursive(PaintLayer* layer, UpdateType upd
     if (layer->stackingNode()->isStackingContext())
         info.ancestorStackingContext = layer;
 
+    if (layer->isRootLayer() || layer->layoutObject()->hasOverflowClip())
+        info.lastOverflowClipLayer = layer;
+
     if (layer->scrollsOverflow())
         info.lastScrollingAncestor = layer;