Fix drag-and-drop autoscrolling with --enable-pinch-virtual-viewport

Source/core/rendering/RenderBox.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 508 matching lines @@
                         // absolute coordinates in the parent.
                         newRect.setX(rect.x() - frameView->scrollX() + frameView->x());
                         newRect.setY(rect.y() - frameView->scrollY() + frameView->y());
                     } else {
                         parentBox = 0;
                     }
                 }
             } else {
                 if (frame()->settings()->pinchVirtualViewportEnabled()) {
                     PinchViewport& pinchViewport = frame()->page()->frameHost().pinchViewport();
-                    LayoutRect r = ScrollAlignment::getRectToExpose(LayoutRect(pinchViewport.visibleRectInDocument()), rect, alignX, alignY);
+
+                    // We want to move the rect into the viewport that excludes the scrollbars so we intersect
+                    // the pinch viewport with the scrollbar-excluded frameView content rect.
+                    LayoutRect viewRect = intersection(
+                        LayoutRect(pinchViewport.visibleRectInDocument()), frameView->visibleContentRect());
+                    LayoutRect r = ScrollAlignment::getRectToExpose(viewRect, rect, alignX, alignY);
+
+                    // pinchViewport.scrollIntoView will attempt to center the given rect within the viewport
+                    // so to prevent it from adjusting r's coordinates the rect must match the viewport's size
+                    // i.e. add the subtracted scrollbars from above back in.
+                    // FIXME: This is hacky and required because getRectToExpose doesn't naturally account
+                    // for the two viewports. crbug.com/449340.
+                    r.setSize(LayoutSize(pinchViewport.visibleRectInDocument().size()));
+
                     pinchViewport.scrollIntoView(r);
                 } else {
                     LayoutRect viewRect = frameView->visibleContentRect();
                     LayoutRect r = ScrollAlignment::getRectToExpose(viewRect, rect, alignX, alignY);
                     frameView->setScrollPosition(DoublePoint(r.location()));
                 }
             }
         }
     }
 
@@ skipping 4017 matching lines @@
     computedValues.m_margins.m_end = marginEnd();
 
     setLogicalTop(oldLogicalTop);
     setLogicalWidth(oldLogicalWidth);
     setLogicalLeft(oldLogicalLeft);
     setMarginLeft(oldMarginLeft);
     setMarginRight(oldMarginRight);
 }
 
 } // namespace blink