Add a setting to do frame scrolls through the root layer.

Source/core/frame/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 2160 matching lines @@
     return page && page->focusController().isActive();
 }
 
 void FrameView::scrollTo(const DoublePoint& newPosition)
 {
     DoublePoint oldPosition = m_scrollPosition;
     DoubleSize scrollDelta = newPosition - oldPosition;
     if (scrollDelta.isZero())
         return;
 
+    if (m_frame->settings() && m_frame->settings()->rootLayerScrolls()) {
+        // Don't scroll the FrameView!
+        ASSERT_NOT_REACHED();
+    }
+
     m_scrollPosition = newPosition;
 
     if (!scrollbarsSuppressed())
         m_pendingScrollDelta += scrollDelta;
 
     updateLayersAndCompositingAfterScrollIfNeeded();
     scrollPositionChanged();
     frame().loader().client()->didChangeScrollOffset();
 }
 
@@ skipping 707 matching lines @@
 {
     bool allowScrolling = userInputScrollable(HorizontalScrollbar) || userInputScrollable(VerticalScrollbar);
 
     // Note that to allow for rubber-band over-scroll behavior, even non-scrollable views
     // should handle wheel events.
 #if !USE(RUBBER_BANDING)
     if (!isScrollable())
         allowScrolling = false;
 #endif
 
+    if (m_frame->settings()->rootLayerScrolls())
+        allowScrolling = false;
+
     if (allowScrolling && ScrollableArea::handleWheelEvent(wheelEvent))
         return true;
 
     // If the frame didn't handle the event, give the pinch-zoom viewport a chance to
     // process the scroll event.
     if (m_frame->settings()->pinchVirtualViewportEnabled() && m_frame->isMainFrame())
         return page()->frameHost().pinchViewport().handleWheelEvent(wheelEvent);
 
     return false;
 }
@@ skipping 323 matching lines @@
 }
 
 void FrameView::computeScrollbarExistence(bool& newHasHorizontalScrollbar, bool& newHasVerticalScrollbar, const IntSize& docSize, ComputeScrollbarExistenceOption option) const
 {
     bool hasHorizontalScrollbar = m_horizontalScrollbar;
     bool hasVerticalScrollbar = m_verticalScrollbar;
 
     newHasHorizontalScrollbar = hasHorizontalScrollbar;
     newHasVerticalScrollbar = hasVerticalScrollbar;
 
+    if (m_frame->settings() && m_frame->settings()->rootLayerScrolls())
+        return;
+
     ScrollbarMode hScroll = m_horizontalScrollbarMode;
     ScrollbarMode vScroll = m_verticalScrollbarMode;
 
     if (hScroll != ScrollbarAuto)
         newHasHorizontalScrollbar = (hScroll == ScrollbarAlwaysOn);
     if (vScroll != ScrollbarAuto)
         newHasVerticalScrollbar = (vScroll == ScrollbarAlwaysOn);
 
     if (m_scrollbarsSuppressed || (hScroll != ScrollbarAuto && vScroll != ScrollbarAuto))
         return;
@@ skipping 480 matching lines @@
     int verticalScrollbarWidth = (verticalScrollbar() && !verticalScrollbar()->isOverlayScrollbar())
         ? verticalScrollbar()->width() : 0;
     int horizontalScrollbarHeight = (horizontalScrollbar() && !horizontalScrollbar()->isOverlayScrollbar())
         ? horizontalScrollbar()->height() : 0;
 
     int physicalScrollY = scrollPosition().y() + scrollOrigin().y();
     if (physicalScrollY < 0) {
         horizontalOverhangRect = frameRect();
         horizontalOverhangRect.setHeight(-physicalScrollY);
         horizontalOverhangRect.setWidth(horizontalOverhangRect.width() - verticalScrollbarWidth);
-    } else if (contentsHeight() && physicalScrollY > contentsHeight() - visibleHeight()) {
+    } else if (physicalScrollY > 0 && contentsHeight() && physicalScrollY > contentsHeight() - visibleHeight()) {
         int height = physicalScrollY - (contentsHeight() - visibleHeight());
         horizontalOverhangRect = frameRect();
         horizontalOverhangRect.setY(frameRect().maxY() - height - horizontalScrollbarHeight);
         horizontalOverhangRect.setHeight(height);
         horizontalOverhangRect.setWidth(horizontalOverhangRect.width() - verticalScrollbarWidth);
     }
 
     int physicalScrollX = scrollPosition().x() + scrollOrigin().x();
     if (physicalScrollX < 0) {
         verticalOverhangRect.setWidth(-physicalScrollX);
         verticalOverhangRect.setHeight(frameRect().height() - horizontalOverhangRect.height() - horizontalScrollbarHeight);
         verticalOverhangRect.setX(frameRect().x());
         if (horizontalOverhangRect.y() == frameRect().y())
             verticalOverhangRect.setY(frameRect().y() + horizontalOverhangRect.height());
         else
             verticalOverhangRect.setY(frameRect().y());
-    } else if (contentsWidth() && physicalScrollX > contentsWidth() - visibleWidth()) {
+    } else if (physicalScrollX > 0 && contentsWidth() && physicalScrollX > contentsWidth() - visibleWidth()) {
         int width = physicalScrollX - (contentsWidth() - visibleWidth());
         verticalOverhangRect.setWidth(width);
         verticalOverhangRect.setHeight(frameRect().height() - horizontalOverhangRect.height() - horizontalScrollbarHeight);
         verticalOverhangRect.setX(frameRect().maxX() - width - verticalScrollbarWidth);
         if (horizontalOverhangRect.y() == frameRect().y())
             verticalOverhangRect.setY(frameRect().y() + horizontalOverhangRect.height());
         else
             verticalOverhangRect.setY(frameRect().y());
     }
 }
@@ skipping 139 matching lines @@
         return;
 
     ScrollableArea::setScrollOrigin(origin);
 
     // Update if the scroll origin changes, since our position will be different if the content size did not change.
     if (updatePositionAtAll && updatePositionSynchronously)
         updateScrollbars(scrollOffsetDouble());
 }
 
 } // namespace blink