Implement scrollbar-gutter on viewports

Source/WebCore/platform/ScrollView.cpp

@@ -36,6 +36,7 @@
 #include "PlatformWheelEvent.h"
 #include "ScrollAnimator.h"
 #include "Scrollbar.h"
+#include "ScrollbarGutter.h"
 #include "ScrollbarTheme.h"
 #include <wtf/HexNumber.h>
 #include <wtf/SetForScope.h>
@@ -441,7 +442,7 @@ void ScrollView::cacheCurrentScrollState()
 ScrollPosition ScrollView::documentScrollPositionRelativeToViewOrigin() const
 {
     return scrollPosition() - IntSize(
-        shouldPlaceVerticalScrollbarOnLeft() && m_verticalScrollbar ? m_verticalScrollbar->occupiedWidth() : 0,
+        (shouldPlaceVerticalScrollbarOnLeft() || scrollbarGutterStyle().bothEdges) ? verticalScrollbarWidth() : 0,
         headerHeight() + topContentInset(TopContentInsetType::WebCoreOrPlatformContentInset));
 }
 
@@ -839,6 +840,33 @@ IntRect ScrollView::rectToCopyOnScroll() const
     return scrollViewRect;
 }
 
+int ScrollView::verticalScrollbarWidth(bool isHorizontalWritingMode) const
+{
+    WTFLogAlways("Test");
+    // TODO should this check overlay scrollbars and return width at the end not occupiedWidth
+
+    if (!m_verticalScrollbar && !(scrollbarGutterStyle().isAuto || ScrollbarTheme::theme().usesOverlayScrollbars()) && isHorizontalWritingMode)
+        return ScrollbarTheme::theme().scrollbarThickness(scrollbarWidthStyle());
+
+    if (!m_verticalScrollbar)
+        return 0;
+
+    return m_verticalScrollbar->occupiedWidth();
+}
+
+int ScrollView::horizontalScrollbarHeight(bool isHorizontalWritingMode) const
+{
+    // TODO should this check overlay scrollbars and return height at the end not occupiedHeight
+
+    if (!m_horizontalScrollbar && !(scrollbarGutterStyle().isAuto || ScrollbarTheme::theme().usesOverlayScrollbars()) && !isHorizontalWritingMode)
+        return ScrollbarTheme::theme().scrollbarThickness(scrollbarWidthStyle());
+
+    if (!m_horizontalScrollbar)
+        return 0;
+
+    return m_horizontalScrollbar->occupiedHeight();
+}
+
 void ScrollView::scrollContents(const IntSize& scrollDelta)
 {
     HostWindow* window = hostWindow();
@@ -1613,8 +1641,8 @@ void ScrollView::styleAndRenderTreeDidChange()
 IntPoint ScrollView::locationOfContents() const
 {
     IntPoint result = location();
-    if (shouldPlaceVerticalScrollbarOnLeft() && m_verticalScrollbar)
-        result.move(m_verticalScrollbar->occupiedWidth(), 0);
+    if ((shouldPlaceVerticalScrollbarOnLeft() || scrollbarGutterStyle().bothEdges))
+        result.move(verticalScrollbarWidth(), 0);
     return result;
 }
 

Source/WebCore/platform/ScrollView.h

@@ -124,6 +124,9 @@ class ScrollView : public Widget, public ScrollableArea {
     void setVerticalScrollbarLock(bool lock = true) { m_verticalScrollbarLock = lock; }
     bool verticalScrollbarLock() const { return m_verticalScrollbarLock; }
 
+    int verticalScrollbarWidth(bool isHorizontalWritingMode = true) const;
+    int horizontalScrollbarHeight(bool isHorizontalWritingMode = true) const;
+
     void setScrollingModesLock(bool lock = true) { m_horizontalScrollbarLock = m_verticalScrollbarLock = lock; }
 
     WEBCORE_EXPORT virtual void setCanHaveScrollbars(bool);

Source/WebCore/rendering/RenderBox.cpp

@@ -918,9 +918,18 @@ bool RenderBox::fixedElementLaysOutRelativeToFrame(const LocalFrameView& frameVi
 
 bool RenderBox::includeVerticalScrollbarSize() const
 {
-    return hasNonVisibleOverflow() && layer() && !layer()->hasOverlayScrollbars()
-        && (style().overflowY() == Overflow::Scroll || style().overflowY() == Overflow::Auto
+    if (layer() && layer()->hasOverlayScrollbars())
+        return false;
+
+    if (hasNonVisibleOverflow()) {
+        return (style().overflowY() == Overflow::Scroll || style().overflowY() == Overflow::Auto
             || (style().overflowY() == Overflow::Hidden && !style().scrollbarGutter().isAuto));
+    }
+
+    if (isDocumentElementRenderer())
+        return !style().scrollbarGutter().isAuto;
+
+    return false;
 }
 
 bool RenderBox::includeHorizontalScrollbarSize() const
@@ -935,6 +944,9 @@ int RenderBox::verticalScrollbarWidth() const
     auto* scrollableArea = layer() ? layer()->scrollableArea() : nullptr;
     if (!scrollableArea)
         return 0;
+
+    if (isDocumentElementRenderer())
+        return includeVerticalScrollbarSize() ? view().frameView().verticalScrollbarWidth(isHorizontalWritingMode()) : 0;
     return includeVerticalScrollbarSize() ? scrollableArea->verticalScrollbarWidth(IgnoreOverlayScrollbarSize, isHorizontalWritingMode()) : 0;
 }