Improve scroll anchoring's interactions with the visual viewport

third_party/WebKit/Source/core/layout/ScrollAnchor.h

Index: third_party/WebKit/Source/core/layout/ScrollAnchor.h
diff --git a/third_party/WebKit/Source/core/layout/ScrollAnchor.h b/third_party/WebKit/Source/core/layout/ScrollAnchor.h
index df5d4c45e3a8151374c8bae0c36cbc4fae4201ca..06ccf0bd6c38fe1c9c4bb7ce0a14c61aa18f2ae0 100644
--- a/third_party/WebKit/Source/core/layout/ScrollAnchor.h
+++ b/third_party/WebKit/Source/core/layout/ScrollAnchor.h
@@ -19,9 +19,17 @@ class CORE_EXPORT ScrollAnchor final {
     DISALLOW_NEW();
 
 public:
-    ScrollAnchor(ScrollableArea*);
+    ScrollAnchor();
+    explicit ScrollAnchor(ScrollableArea*);
     ~ScrollAnchor();
 
+    // The scroller that is scrolled to componsate for layout movements. Note
+    // that the scroller can only be initialized once.
+    void setScroller(ScrollableArea*);
+
+    // Returns true if the underlying scroller is set.
+    bool hasScroller() const { return m_scroller; }
+
     // The LayoutObject we are currently anchored to. Lazily computed during
     // save() and cached until the next call to clear().
     LayoutObject* anchorObject() const { return m_current.m_anchorObject; }