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..b87e15cbed28e44fec7c60dd1dafdf0fa7a12af2 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();
 
@@ -679,15 +686,17 @@ 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())
-            setHasHorizontalScrollbar(hasHorizontalOverflow);
-        if (box().hasAutoVerticalScrollbar())
-            setHasVerticalScrollbar(hasVerticalOverflow);
+    // overflow:auto may need to lay out again if scrollbars got added/removed and even on reconstruction of scrollbars

[skobes, 2015/08/19 19:40:18]

Rephrase this comment:

    // We need to layout again if scrollbars are added or removed by
overflow:auto,
    // or by changing between native and custom.

[MuVen, 2015/08/19 20:37:33]

Done.

+    // from native to custom or vice versa also needs to layout again.
+    bool horizontalScrollBarChanged = (box().hasAutoHorizontalScrollbar() && (hasHorizontalScrollbar() != hasHorizontalOverflow))
+    || (box().style()->overflowX() == OSCROLL && !horizontalScrollbar());

[skobes, 2015/08/19 19:40:17]

fix indentation

[MuVen, 2015/08/19 20:37:33]

Done.

+    bool verticalScrollBarChanged = (box().hasAutoVerticalScrollbar() && (hasVerticalScrollbar() != hasVerticalOverflow))
+    || (box().style()->overflowY() == OSCROLL && !verticalScrollbar());
+    if (!visualViewportSuppliesScrollbars() && (horizontalScrollBarChanged || verticalScrollBarChanged)) {
+        if (box().hasAutoHorizontalScrollbar() || (box().style()->overflowX() == OSCROLL && !horizontalScrollbar()))
+            setHasHorizontalScrollbar(true);

[skobes, 2015/08/19 19:40:18]

This still looks wrong.  Auto and OSCROLL are separate cases.  In the auto case,
we want to pass the value of hasHorizontalOverflow.  In the OSCROLL case, we
want to pass true.

[MuVen, 2015/08/19 20:37:33]

True, Miss-read your previous comment, Even i was thinking the same But just
followed your earlier comment.

+        if (box().hasAutoVerticalScrollbar() || (box().style()->overflowY() == OSCROLL && !verticalScrollbar()))
+            setHasVerticalScrollbar(true);
 
         if (hasVerticalOverflow || hasHorizontalOverflow)
             updateScrollCornerStyle();
@@ -698,15 +707,15 @@ void DeprecatedPaintLayerScrollableArea::updateAfterLayout()
         if (box().document().hasAnnotatedRegions())
             box().document().setAnnotatedRegionsDirty(true);
 
-        if (box().style()->overflowX() == OAUTO || box().style()->overflowY() == OAUTO) {
+        // Our proprietary overflow: overlay value doesn't trigger a layout.
+        if ((horizontalScrollBarChanged && box().style()->overflowX() != OOVERLAY) || (verticalScrollBarChanged && box().style()->overflowY() != OOVERLAY)) {
             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.scrollbarsChanged(horizontalScrollBarChanged, verticalScrollBarChanged);
                     block.layoutBlock(true);
                 } else {
                     box().layout();
@@ -958,6 +967,15 @@ 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;