Recompute slow scroll regions after overflow recalc

Source/core/page/scrolling/ScrollingCoordinator.cpp

 /*
  * Copyright (C) 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 111 matching lines @@
     }
 }
 
 void ScrollingCoordinator::notifyLayoutUpdated()
 {
     m_scrollGestureRegionIsDirty = true;
     m_touchEventTargetRectsAreDirty = true;
     m_shouldScrollOnMainThreadDirty = true;
 }
 
+void ScrollingCoordinator::notifyOverflowUpdated()
+{
+    m_scrollGestureRegionIsDirty = true;
+}
+
 void ScrollingCoordinator::scrollableAreasDidChange()
 {
     ASSERT(m_page);
     if (!m_page->mainFrame()->isLocalFrame() || !m_page->deprecatedLocalMainFrame()->view())
         return;
 
     // Layout may update scrollable area bounding boxes. It also sets the same dirty
     // flag making this one redundant (See |ScrollingCoordinator::notifyLayoutUpdated|).
     // So if layout is expected, ignore this call allowing scrolling coordinator
     // to be notified post-layout to recompute gesture regions.
@@ skipping 919 matching lines @@
     bool frameIsScrollable = frameView && frameView->isScrollable();
     if (frameIsScrollable != m_wasFrameScrollable)
         return true;
 
     if (WebLayer* scrollLayer = frameView ? toWebLayer(frameView->layerForScrolling()) : nullptr)
         return WebSize(frameView->contentsSize()) != scrollLayer->bounds();
     return false;
 }
 
 } // namespace blink