Fixed Inconsistent behaviour of custom-scrollbar

Source/core/frame/FrameView.cpp

Index: Source/core/frame/FrameView.cpp
diff --git a/Source/core/frame/FrameView.cpp b/Source/core/frame/FrameView.cpp
index 0de05a9afddf16597794d73fd931bbfc17820627..beb1677547861812d27a329ad8e993734f830f02 100644
--- a/Source/core/frame/FrameView.cpp
+++ b/Source/core/frame/FrameView.cpp
@@ -1698,7 +1698,7 @@ void FrameView::contentsResized()
     setNeedsLayout();
 }
 
-void FrameView::scrollbarExistenceDidChange()
+void FrameView::scrollbarNeedsLayout()
 {
     // We check to make sure the view is attached to a frame() as this method can
     // be triggered before the view is attached by LocalFrame::createView(...) setting
@@ -3310,6 +3310,8 @@ void FrameView::updateScrollbarGeometry()
         if (!m_scrollbarsSuppressed && oldRect != m_horizontalScrollbar->frameRect())
             m_horizontalScrollbar->invalidate();
 
+        oldRect = m_horizontalScrollbar->frameRect();
+
         if (m_scrollbarsSuppressed)
             m_horizontalScrollbar->setSuppressInvalidation(true);
         m_horizontalScrollbar->setEnabled(contentsWidth() > clientWidth);
@@ -3317,6 +3319,17 @@ void FrameView::updateScrollbarGeometry()
         m_horizontalScrollbar->offsetDidChange();
         if (m_scrollbarsSuppressed)
             m_horizontalScrollbar->setSuppressInvalidation(false);
+
+        if (!m_scrollbarsSuppressed && oldRect != m_horizontalScrollbar->frameRect() && m_horizontalScrollbar->isCustomScrollbar()) {
+            IntRect hBarRect((shouldPlaceVerticalScrollbarOnLeft() && m_verticalScrollbar) ? m_verticalScrollbar->width() : 0,
+                height() - m_horizontalScrollbar->height(),
+                width() - (m_verticalScrollbar ? m_verticalScrollbar->width() : 0),
+                m_horizontalScrollbar->height());
+            m_horizontalScrollbar->setFrameRect(adjustScrollbarRectForResizer(hBarRect, m_horizontalScrollbar.get()));
+            if (oldRect.height() != m_horizontalScrollbar->frameRect().height())
+                scrollbarNeedsLayout();
+            m_horizontalScrollbar->invalidate();
+        }
     }
 
     if (m_verticalScrollbar) {
@@ -3330,6 +3343,8 @@ void FrameView::updateScrollbarGeometry()
         if (!m_scrollbarsSuppressed && oldRect != m_verticalScrollbar->frameRect())
             m_verticalScrollbar->invalidate();
 
+        oldRect = m_verticalScrollbar->frameRect();
+
         if (m_scrollbarsSuppressed)
             m_verticalScrollbar->setSuppressInvalidation(true);
         m_verticalScrollbar->setEnabled(contentsHeight() > clientHeight);
@@ -3337,6 +3352,17 @@ void FrameView::updateScrollbarGeometry()
         m_verticalScrollbar->offsetDidChange();
         if (m_scrollbarsSuppressed)
             m_verticalScrollbar->setSuppressInvalidation(false);
+
+        if (!m_scrollbarsSuppressed && oldRect != m_verticalScrollbar->frameRect() && m_verticalScrollbar->isCustomScrollbar()) {
+            IntRect vBarRect(shouldPlaceVerticalScrollbarOnLeft() ? 0 : (width() - m_verticalScrollbar->width()),
+                0,
+                m_verticalScrollbar->width(),
+                height() - (m_horizontalScrollbar ? m_horizontalScrollbar->height() : 0));
+            m_verticalScrollbar->setFrameRect(adjustScrollbarRectForResizer(vBarRect, m_verticalScrollbar.get()));
+            if (oldRect.width() != m_verticalScrollbar->frameRect().width())
+                scrollbarNeedsLayout();
+            m_verticalScrollbar->invalidate();
+        }
     }
 }
 
@@ -3379,7 +3405,7 @@ bool FrameView::adjustScrollbarExistence(ComputeScrollbarExistenceOption option)
     // first.  (This will be the common case, e.g., when the page changes due to window resizing for example).
     // This layout will not re-enter updateScrollbars and does not count towards our max layout pass total.
     if (!m_scrollbarsSuppressed)
-        scrollbarExistenceDidChange();
+        scrollbarNeedsLayout();
 
     bool hasHorizontalScrollbar = m_horizontalScrollbar;
     bool hasVerticalScrollbar = m_verticalScrollbar;
@@ -3400,7 +3426,7 @@ bool FrameView::adjustScrollbarExistence(ComputeScrollbarExistenceOption option)
 
     if (!useOverlayScrollbars())
         contentsResized();
-    scrollbarExistenceDidChange();
+    scrollbarNeedsLayout();
     return true;
 }