Adds DevTools commands for forced viewport override.

third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@gmail.com>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 395 matching lines @@
     if (box().node())
         box().node()->document().enqueueScrollEventForNode(box().node());
 
     if (AXObjectCache* cache = box().document().existingAXObjectCache())
         cache->handleScrollPositionChanged(&box());
     box().view()->clearHitTestCache();
 
     // Inform the FrameLoader of the new scroll position, so it can be restored when navigating back.
     if (layer()->isRootLayer()) {
         frameView->frame().loader().saveScrollState();
-        frame->loader().client()->didChangeScrollOffset();
+        frameView->didChangeScrollOffset();
     }
 
     // All scrolls clear the fragment anchor.
     frameView->clearFragmentAnchor();
 
     // Clear the scroll anchor, unless it is the reason for this scroll.
     if (RuntimeEnabledFeatures::scrollAnchoringEnabled() && scrollType != AnchoringScroll)
         scrollAnchor()->clear();
 }
 
@@ skipping 1341 matching lines @@
 
 void PaintLayerScrollableArea::DelayScrollPositionClampScope::clampScrollableAreas()
 {
     for (auto& scrollableArea : *s_needsClamp)
         scrollableArea->clampScrollPositionsAfterLayout();
     delete s_needsClamp;
     s_needsClamp = nullptr;
 }
 
 } // namespace blink