Root layer scrolling: set correct size for document's main GraphicsLayer.

third_party/WebKit/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 1235 matching lines @@
     if (m_viewportConstrainedObjects && m_viewportConstrainedObjects->contains(object)) {
         m_viewportConstrainedObjects->remove(object);
 
         if (ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator())
             scrollingCoordinator->frameViewFixedObjectsDidChange(this);
     }
 }
 
 void FrameView::viewportSizeChanged(bool widthChanged, bool heightChanged)
 {
+    if (m_frame->settings() && m_frame->settings()->rootLayerScrolls()) {
+        // The background must be repainted when the FrameView is resized, even if the initial
+        // containing block does not change (so we can't rely on layout to issue the invalidation).
+        // This is because the background fills the main GraphicsLayer, which takes the size of the
+        // layout viewport.
+        // TODO(skobes): Paint non-fixed backgrounds into the scrolling contents layer and avoid
+        // this invalidation (http://crbug.com/568847).
+        if (LayoutView* lv = layoutView())
+            lv->setShouldDoFullPaintInvalidation();
+    }
+
     if (!hasViewportConstrainedObjects())
         return;
 
     for (const auto& viewportConstrainedObject : *m_viewportConstrainedObjects) {
         LayoutObject* layoutObject = viewportConstrainedObject;
         const ComputedStyle& style = layoutObject->styleRef();
         if (widthChanged) {
             if (style.width().isFixed() && (style.left().isAuto() || style.right().isAuto()))
                 layoutObject->setNeedsPositionedMovementLayout();
             else
@@ skipping 2742 matching lines @@
     return m_hiddenForThrottling && m_crossOriginForThrottling;
 }
 
 LayoutBox& FrameView::boxForScrollControlPaintInvalidation() const
 {
     ASSERT(layoutView());
     return *layoutView();
 }
 
 } // namespace blink