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..cb96550357f76c0ff46d4b17c0e2a2b989927d16 100644
--- a/Source/core/paint/DeprecatedPaintLayerScrollableArea.cpp
+++ b/Source/core/paint/DeprecatedPaintLayerScrollableArea.cpp
@@ -646,6 +646,16 @@ void DeprecatedPaintLayerScrollableArea::updateAfterLayout()
 {
     ASSERT(box().hasOverflowClip());
 
+    bool isScrollbarReconstructionRequired = needsScrollbarReconstruction();
+    if (m_hBar && !m_hBar->isCustomScrollbar() && isScrollbarReconstructionRequired) {
+        destroyScrollbar(HorizontalScrollbar);

[MuVen, 2015/08/13 19:36:32]

!m_hBar->isCustomScrollbar() This condition wont trigger reconstruction
every-time after layout. May be i see i need to pull all these conditions in the
needsScrollbarReconstruction logic. wdyt about the api calls in the if loop. is
that fine to call destroyScrollbar and call setHasHorizontalScrollbar(true) ? or

setHasHorizontalScrollbar(false);
setHasHorizontalScrollbar(true);

please share your inputs.

[skobes, 2015/08/13 19:53:43]

Yes, to make it easier to follow, needsScrollbarReconstruction should return
true if and only if one or both scrollbars need to be reconstructed.
I think if any scrollbar needs reconstruction it should be sufficient to destroy
them both, then let the regular overflow logic create them again below.

+        setHasHorizontalScrollbar(true);
+    }
+    if (m_vBar && !m_vBar->isCustomScrollbar() && isScrollbarReconstructionRequired) {
+        destroyScrollbar(VerticalScrollbar);
+        setHasVerticalScrollbar(true);
+    }
+
     DoubleSize originalScrollOffset = adjustedScrollOffset();
     computeScrollDimensions();
 
@@ -958,6 +968,12 @@ static inline LayoutObject* layoutObjectForScrollbar(LayoutObject& layoutObject)
     return &layoutObject;
 }
 
+bool DeprecatedPaintLayerScrollableArea::needsScrollbarReconstruction() const
+{
+    LayoutObject* actualLayoutObject = layoutObjectForScrollbar(box());
+    return actualLayoutObject->isBox() && actualLayoutObject->style()->hasPseudoStyle(SCROLLBAR);

[skobes, 2015/08/13 18:12:40]

This will reconstruct custom scrollbars after every layout.  We only want to
reconstruct if the scrollbar is currently native, and should be custom, or if it
is currently custom, and should be native.

+}
+
 PassRefPtrWillBeRawPtr<Scrollbar> DeprecatedPaintLayerScrollableArea::createScrollbar(ScrollbarOrientation orientation)
 {
     RefPtrWillBeRawPtr<Scrollbar> widget = nullptr;