Create custom scrollbars when html element has overflow:scroll

Source/core/paint/DeprecatedPaintLayerScrollableArea.cpp

Index: Source/core/paint/DeprecatedPaintLayerScrollableArea.cpp
diff --git a/Source/core/paint/DeprecatedPaintLayerScrollableArea.cpp b/Source/core/paint/DeprecatedPaintLayerScrollableArea.cpp
index 75b2999646e092109c931114f7a27add34ba4c50..d3d4ae65f767ab64ae883ce64b0e8ab7522ef266 100644
--- a/Source/core/paint/DeprecatedPaintLayerScrollableArea.cpp
+++ b/Source/core/paint/DeprecatedPaintLayerScrollableArea.cpp
@@ -646,6 +646,13 @@ void DeprecatedPaintLayerScrollableArea::updateAfterLayout()
 {
     ASSERT(box().hasOverflowClip());
 
+    if (needsScrollbarReconstruction()) {
+        if (m_hBar)
+            destroyScrollbar(HorizontalScrollbar);
+        if (m_vBar)
+            destroyScrollbar(VerticalScrollbar);
+    }
+
     DoubleSize originalScrollOffset = adjustedScrollOffset();
     computeScrollDimensions();
 
@@ -679,14 +686,14 @@ void DeprecatedPaintLayerScrollableArea::updateAfterLayout()
         if (!scrollSize(VerticalScrollbar))
             setHasVerticalScrollbar(false);
     }
-    // overflow:auto may need to lay out again if scrollbars got added/removed.
-    bool autoHorizontalScrollBarChanged = box().hasAutoHorizontalScrollbar() && (hasHorizontalScrollbar() != hasHorizontalOverflow);
-    bool autoVerticalScrollBarChanged = box().hasAutoVerticalScrollbar() && (hasVerticalScrollbar() != hasVerticalOverflow);
-
-    if (!visualViewportSuppliesScrollbars() && (autoHorizontalScrollBarChanged || autoVerticalScrollBarChanged)) {
-        if (box().hasAutoHorizontalScrollbar())
+    // overflow:auto may need to lay out again if scrollbars got added/removed and even on reconstruction of scrollbars
+    // from native to custom or vice versa also needs to layout again.
+    bool horizontalScrollBarChanged = (box().hasAutoHorizontalScrollbar() && (hasHorizontalScrollbar() != hasHorizontalOverflow)) || (box().style()->overflowX() == OSCROLL && !horizontalScrollbar());
+    bool verticalScrollBarChanged = (box().hasAutoVerticalScrollbar() && (hasVerticalScrollbar() != hasVerticalOverflow)) || (box().style()->overflowY() == OSCROLL && !verticalScrollbar());
+    if (!visualViewportSuppliesScrollbars() && (horizontalScrollBarChanged || verticalScrollBarChanged)) {
+        if (box().hasAutoHorizontalScrollbar() || box().style()->overflowX() == OSCROLL)

[MuVen, 2015/08/18 13:20:01]

in case of overflow-x:scroll and overflow-y:auto, for ex
LayoutTests/scrollbars/disabled-scrollbar.html
overflow logic during styling has calculated horizontal scrollbar, but as not
overflow of contents, thumb
is not shown, just painted the track. 

Think that verticalScrollbarChanged, 
horizontalScrollBarChanged = 0 verticalScrollBarChanged = 1

but the below condition will be executed, as overflow-x:scroll and doesnt has
horizontalOverflow. This disables
the scrollbar. I think its better we add && !horizontalScrollbar() check.
           
		   if (box().hasAutoHorizontalScrollbar() ||box().style()->overflowX() ==
OSCROLL)  {
            setHasHorizontalScrollbar(hasHorizontalOverflow);

             setHasHorizontalScrollbar(hasHorizontalOverflow);
-        if (box().hasAutoVerticalScrollbar())
+        if (box().hasAutoVerticalScrollbar() || box().style()->overflowY() == OSCROLL)
             setHasVerticalScrollbar(hasVerticalOverflow);
 
         if (hasVerticalOverflow || hasHorizontalOverflow)
@@ -698,21 +705,19 @@ void DeprecatedPaintLayerScrollableArea::updateAfterLayout()
         if (box().document().hasAnnotatedRegions())
             box().document().setAnnotatedRegionsDirty(true);
 
-        if (box().style()->overflowX() == OAUTO || box().style()->overflowY() == OAUTO) {
-            if (!m_inOverflowRelayout) {
-                // Our proprietary overflow: overlay value doesn't trigger a layout.
-                m_inOverflowRelayout = true;
-                SubtreeLayoutScope layoutScope(box());
-                layoutScope.setNeedsLayout(&box(), LayoutInvalidationReason::ScrollbarChanged);
-                if (box().isLayoutBlock()) {
-                    LayoutBlock& block = toLayoutBlock(box());
-                    block.scrollbarsChanged(autoHorizontalScrollBarChanged, autoVerticalScrollBarChanged);
-                    block.layoutBlock(true);
-                } else {
-                    box().layout();
-                }
-                m_inOverflowRelayout = false;
+        if (!m_inOverflowRelayout) {
+            // Our proprietary overflow: overlay value doesn't trigger a layout.
+            m_inOverflowRelayout = true;
+            SubtreeLayoutScope layoutScope(box());
+            layoutScope.setNeedsLayout(&box(), LayoutInvalidationReason::ScrollbarChanged);
+            if (box().isLayoutBlock()) {
+                LayoutBlock& block = toLayoutBlock(box());
+                block.scrollbarsChanged(horizontalScrollBarChanged, verticalScrollBarChanged);
+                block.layoutBlock(true);
+            } else {
+                box().layout();
             }
+            m_inOverflowRelayout = false;
         }
     }
 
@@ -958,6 +963,15 @@ static inline LayoutObject* layoutObjectForScrollbar(LayoutObject& layoutObject)
     return &layoutObject;
 }
 
+bool DeprecatedPaintLayerScrollableArea::needsScrollbarReconstruction() const
+{
+    LayoutObject* actualLayoutObject = layoutObjectForScrollbar(box());
+    bool shouldUseCustom = actualLayoutObject->isBox() && actualLayoutObject->style()->hasPseudoStyle(SCROLLBAR);
+    bool hasAnyScrollbar = hasScrollbar();
+    bool hasCustom = (m_hBar && m_hBar->isCustomScrollbar()) || (m_vBar && m_vBar->isCustomScrollbar());
+    return hasAnyScrollbar && (shouldUseCustom != hasCustom);
+}
+
 PassRefPtrWillBeRawPtr<Scrollbar> DeprecatedPaintLayerScrollableArea::createScrollbar(ScrollbarOrientation orientation)
 {
     RefPtrWillBeRawPtr<Scrollbar> widget = nullptr;