Allow objects without scrollbars to be scrollable

Source/core/rendering/RenderLayer.cpp

Index: Source/core/rendering/RenderLayer.cpp
diff --git a/Source/core/rendering/RenderLayer.cpp b/Source/core/rendering/RenderLayer.cpp
index 70f6a3e44e358bdcd4586651d1ec5fb1fe8afff1..b7a7b4dcb1a71e8581955d8ced29b10983ca54d7 100644
--- a/Source/core/rendering/RenderLayer.cpp
+++ b/Source/core/rendering/RenderLayer.cpp
@@ -1329,6 +1329,29 @@ IntRect RenderLayer::scrollableAreaBoundingBox() const
     return renderer()->absoluteBoundingBoxRect();
 }
 
+bool RenderLayer::userInputScrollable(ScrollbarOrientation orientation) const
+{
+    RenderBox* box = renderBox();
+    ASSERT(box);
+
+    EOverflow overflowStyle = (orientation == HorizontalScrollbar) ?
+        renderer()->style()->overflowX() : renderer()->style()->overflowY();
+    return (overflowStyle == OSCROLL || overflowStyle == OAUTO);
+}
+
+int RenderLayer::pageStep(ScrollbarOrientation orientation) const
+{
+    RenderBox* box = renderBox();
+    ASSERT(box);
+
+    int length = (orientation == HorizontalScrollbar) ?
+        box->pixelSnappedClientWidth() : box->pixelSnappedClientHeight();
+    int minPageStep = static_cast<float>(length) * ScrollableArea::minFractionToStepWhenPaging();
+    int pageStep = max(minPageStep, length - ScrollableArea::maxOverlapBetweenPages());
+
+    return max(pageStep, 1);
+}
+
 RenderLayer* RenderLayer::enclosingTransformedAncestor() const
 {
     RenderLayer* curr = parent();
@@ -2489,8 +2512,13 @@ void RenderLayer::resize(const PlatformEvent& evt, const LayoutSize& oldOffset)
 
 int RenderLayer::scrollSize(ScrollbarOrientation orientation) const
 {
-    Scrollbar* scrollbar = ((orientation == HorizontalScrollbar) ? m_hBar : m_vBar).get();
-    return scrollbar ? (scrollbar->totalSize() - scrollbar->visibleSize()) : 0;
+    RenderBox* box = renderBox();
+    ASSERT(box);
+
+    if (orientation == HorizontalScrollbar)
+        return m_scrollSize.width() - box->pixelSnappedClientWidth();
+
+    return m_scrollSize.height() - box->pixelSnappedClientHeight();
 }
 
 int RenderLayer::scrollPosition(Scrollbar* scrollbar) const
@@ -2860,14 +2888,6 @@ void RenderLayer::destroyScrollbar(ScrollbarOrientation orientation)
     scrollbar = 0;
 }
 
-bool RenderLayer::scrollsOverflow() const
-{
-    if (!renderer()->isBox())
-        return false;
-
-    return toRenderBox(renderer())->scrollsOverflow();
-}
-
 void RenderLayer::setHasHorizontalScrollbar(bool hasScrollbar)
 {
     if (hasScrollbar == hasHorizontalScrollbar())
@@ -3126,14 +3146,10 @@ void RenderLayer::updateScrollbarsAfterLayout()
     // Set up the range (and page step/line step).
     if (m_hBar) {
         int clientWidth = box->pixelSnappedClientWidth();
-        int pageStep = max(max<int>(clientWidth * Scrollbar::minFractionToStepWhenPaging(), clientWidth - Scrollbar::maxOverlapBetweenPages()), 1);
-        m_hBar->setSteps(Scrollbar::pixelsPerLineStep(), pageStep);
         m_hBar->setProportion(clientWidth, m_scrollSize.width());
     }
     if (m_vBar) {
         int clientHeight = box->pixelSnappedClientHeight();
-        int pageStep = max(max<int>(clientHeight * Scrollbar::minFractionToStepWhenPaging(), clientHeight - Scrollbar::maxOverlapBetweenPages()), 1);
-        m_vBar->setSteps(Scrollbar::pixelsPerLineStep(), pageStep);
         m_vBar->setProportion(clientHeight, m_scrollSize.height());
     }