Normalize top controls offset to (0, 1), Blink-side.

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 3068 matching lines @@
 {
     ScrollableArea::willRemoveScrollbar(scrollbar, orientation);
     if (AXObjectCache* cache = axObjectCache()) {
         cache->remove(scrollbar);
         cache->handleScrollbarUpdate(this);
     }
 }
 
 void FrameView::setTopControlsViewportAdjustment(float adjustment)
 {
-#if !OS(ANDROID)
-    // The adjustment is done only for top controls which are android only.
-    ASSERT(!adjustment);
-#endif
     m_topControlsViewportAdjustment = adjustment;
 }
 
 IntPoint FrameView::maximumScrollPosition() const
 {
     // Make the same calculation as in CC's LayerImpl::MaxScrollOffset()
     // FIXME: We probably shouldn't be storing the bounds in a float. crbug.com/422331.
     FloatSize visibleSize = unscaledVisibleContentSize(ExcludeScrollbars);
     visibleSize.expand(0, m_topControlsViewportAdjustment);
 
@@ skipping 935 matching lines @@
 {
     Settings* settings = frame().settings();
     if (!settings || !settings->rootLayerScrolls())
         return this;
 
     RenderView* renderView = this->renderView();
     return renderView ? renderView->scrollableArea() : nullptr;
 }
 
 } // namespace blink