OverscrollGlow for mainThread-{BLINK CHANGES}

Source/core/page/EventHandler.h

Index: Source/core/page/EventHandler.h
diff --git a/Source/core/page/EventHandler.h b/Source/core/page/EventHandler.h
index b57b8abc3a3ff1afd8c352a1d8ad284d7226e89a..67745e764098da8b9c4704cdb92e803fccf9ffea 100644
--- a/Source/core/page/EventHandler.h
+++ b/Source/core/page/EventHandler.h
@@ -128,6 +128,9 @@ public:
 
     void resizeScrollableAreaDestroyed();
 
+    FloatSize unusedDeltaForTesting() const { return m_unusedDelta; }
+    FloatSize accumulatedRootOverscrollForTesting() const { return m_accumulatedRootOverscroll; }
+
     IntPoint lastKnownMousePosition() const;
 
     // Attempts to scroll the DOM tree. If that fails, scrolls the view.
@@ -261,7 +264,7 @@ private:
     //            On output, if provided and a node was scrolled stopNode will point to that node.
     // delta - The delta to scroll by, in the units of the granularity parameter. (e.g. pixels, lines, pages, etc.)
     // absolutePoint - For wheel scrolls - the location, in absolute coordinates, where the event occured.
-    bool scroll(ScrollDirection, ScrollGranularity, Node* startNode = nullptr, Node** stopNode = nullptr, float delta = 1.0f, IntPoint absolutePoint = IntPoint());
+    ScrollResultOneDimensional scroll(ScrollDirection, ScrollGranularity, Node* startNode = nullptr, Node** stopNode = nullptr, float delta = 1.0f, IntPoint absolutePoint = IntPoint());
 
     void customizedScroll(const Node& startNode, ScrollState&);
 
@@ -378,6 +381,9 @@ private:
 
     LayoutSize m_offsetFromResizeCorner; // In the coords of m_resizeScrollableArea.
 
+    FloatSize m_unusedDelta;
+    FloatSize m_accumulatedRootOverscroll;
+
     bool m_mousePositionIsUnknown;
     // The last mouse movement position this frame has seen in root frame coordinates.
     IntPoint m_lastKnownMousePosition;