Allow objects without scrollbars to be scrollable

Source/web/ScrollbarGroup.cpp

Index: Source/web/ScrollbarGroup.cpp
diff --git a/Source/web/ScrollbarGroup.cpp b/Source/web/ScrollbarGroup.cpp
index 3fa766eb82ec47b613fa053f8b428a105ef5bd5e..f44ec53d67af4d33f50ec5c4575114ebedd6ea9f 100644
--- a/Source/web/ScrollbarGroup.cpp
+++ b/Source/web/ScrollbarGroup.cpp
@@ -100,14 +100,6 @@ int ScrollbarGroup::scrollSize(WebCore::ScrollbarOrientation orientation) const
     return scrollbar->totalSize() - scrollbar->visibleSize();
 }
 
-int ScrollbarGroup::scrollPosition(Scrollbar* scrollbar) const
-{
-    WebPluginScrollbarImpl* webScrollbar = scrollbar->orientation() == HorizontalScrollbar ? m_horizontalScrollbar : m_verticalScrollbar;
-    if (!webScrollbar)
-        return 0;
-    return webScrollbar->scrollOffset();
-}
-
 void ScrollbarGroup::setScrollOffset(const IntPoint& offset)
 {
     if (m_horizontalScrollbar && m_horizontalScrollbar->scrollOffset() != offset.x())
@@ -268,4 +260,31 @@ bool ScrollbarGroup::scrollbarsCanBeActive() const
     return true;
 }
 
+bool ScrollbarGroup::userInputScrollable(ScrollbarOrientation orientation) const
+{
+    return orientation == HorizontalScrollbar ? horizontalScrollbar() : verticalScrollbar();
+}
+
+int ScrollbarGroup::pageStep(ScrollbarOrientation orientation) const
+{
+    int length;
+    if (orientation == VerticalScrollbar) {
+        if (!m_verticalScrollbar)
+            return 0;
+
+        length = m_verticalScrollbar->scrollbar()->height();
+    } else {
+        if (!m_horizontalScrollbar)
+            return 0;
+
+        length = m_horizontalScrollbar->scrollbar()->width();
+    }
+
+    int pageStep = std::max(
+        static_cast<int>(static_cast<float>(length) * ScrollableArea::minFractionToStepWhenPaging()),
+        length - ScrollableArea::maxOverlapBetweenPages());
+
+    return std::max(pageStep, 1);
+}
+
 } // namespace WebKit