1 files changed, 20 insertions, 5 deletions
diff --git a/Source/WebCore/platform/ScrollableArea.cpp b/Source/WebCore/platform/ScrollableArea.cpp
index 00017bd..34cec9e 100644
--- a/Source/WebCore/platform/ScrollableArea.cpp
+++ b/Source/WebCore/platform/ScrollableArea.cpp
@@ -128,17 +128,26 @@ void ScrollableArea::setScrollOffsetFromAnimation(const IntPoint& offset)
     // Tell the derived class to scroll its contents.
     setScrollOffset(offset);
 
-    bool hasOverlayScrollbars = ScrollbarTheme::nativeTheme()->usesOverlayScrollbars();
+    Scrollbar* verticalScrollbar = this->verticalScrollbar();
 
     // Tell the scrollbars to update their thumb postions.
     if (Scrollbar* horizontalScrollbar = this->horizontalScrollbar()) {
         horizontalScrollbar->offsetDidChange();
-        if (hasOverlayScrollbars)
-            horizontalScrollbar->invalidate();
+        if (horizontalScrollbar->isOverlayScrollbar()) {
+            if (!verticalScrollbar)
+                horizontalScrollbar->invalidate();
+            else {
+                // If there is both a horizontalScrollbar and a verticalScrollbar,
+                // then we must also invalidate the corner between them.
+                IntRect boundsAndCorner = horizontalScrollbar->boundsRect();
+                boundsAndCorner.setWidth(boundsAndCorner.width() + verticalScrollbar->width());
+                horizontalScrollbar->invalidateRect(boundsAndCorner);
+            }
+        }
     }
-    if (Scrollbar* verticalScrollbar = this->verticalScrollbar()) {
+    if (verticalScrollbar) {
         verticalScrollbar->offsetDidChange();
-        if (hasOverlayScrollbars)
+        if (verticalScrollbar->isOverlayScrollbar())
             verticalScrollbar->invalidate();
     }
 }
@@ -179,4 +188,10 @@ void ScrollableArea::willRemoveHorizontalScrollbar(Scrollbar* scrollbar)
     scrollAnimator()->willRemoveHorizontalScrollbar(scrollbar);
 }
 
+bool ScrollableArea::hasOverlayScrollbars() const
+{
+    return (verticalScrollbar() && verticalScrollbar()->isOverlayScrollbar())
+        || (horizontalScrollbar() && horizontalScrollbar()->isOverlayScrollbar());
+}
+
 } // namespace WebCore