Allow objects without scrollbars to be scrollable

Source/web/ScrollbarGroup.cpp

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 82 matching lines @@
 
 int ScrollbarGroup::scrollSize(WebCore::ScrollbarOrientation orientation) const
 {
     WebPluginScrollbarImpl* webScrollbar = orientation == HorizontalScrollbar ? m_horizontalScrollbar : m_verticalScrollbar;
     if (!webScrollbar)
         return 0;
     Scrollbar* scrollbar = webScrollbar->scrollbar();
     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())
         m_horizontalScrollbar->setScrollOffset(offset.x());
     else if (m_verticalScrollbar && m_verticalScrollbar->scrollOffset() != offset.y())
         m_verticalScrollbar->setScrollOffset(offset.y());
 }
 
 void ScrollbarGroup::invalidateScrollbarRect(Scrollbar* scrollbar, const IntRect& rect)
 {
@@ skipping 140 matching lines @@
         m_horizontalScrollbar->scrollbarStyleChanged();
     if (m_verticalScrollbar)
         m_verticalScrollbar->scrollbarStyleChanged();
 }
 
 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