Reland main thread position sticky implementation.

third_party/WebKit/Source/core/frame/FrameView.h

Index: third_party/WebKit/Source/core/frame/FrameView.h
diff --git a/third_party/WebKit/Source/core/frame/FrameView.h b/third_party/WebKit/Source/core/frame/FrameView.h
index 1bcdcdf0bb9b8a3f1ae8e9ee26729a260985b927..8ed74dcd2c69d818f0058ea6cbb1e4aa4dcb42cb 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.h
+++ b/third_party/WebKit/Source/core/frame/FrameView.h
@@ -201,6 +201,11 @@ public:
     const ViewportConstrainedObjectSet* viewportConstrainedObjects() const { return m_viewportConstrainedObjects.get(); }
     bool hasViewportConstrainedObjects() const { return m_viewportConstrainedObjects && m_viewportConstrainedObjects->size() > 0; }
 
+    // Sticky objects.
+    void addStickyPositionObject() { ++m_stickyPositionObjectCount; }
+    void removeStickyPositionObject() { --m_stickyPositionObjectCount; }
+    bool hasStickyPositionObjects() const { return m_stickyPositionObjectCount; }
+
     // Objects with background-attachment:fixed.
     void addBackgroundAttachmentFixedObject(LayoutObject*);
     void removeBackgroundAttachmentFixedObject(LayoutObject*);
@@ -824,6 +829,7 @@ private:
     Member<ScrollableAreaSet> m_animatingScrollableAreas;
     OwnPtr<ResizerAreaSet> m_resizerAreas;
     OwnPtr<ViewportConstrainedObjectSet> m_viewportConstrainedObjects;
+    unsigned m_stickyPositionObjectCount;
     ViewportConstrainedObjectSet m_backgroundAttachmentFixedObjects;
     Member<FrameViewAutoSizeInfo> m_autoSizeInfo;