Fix main thread top controls scrolling to mirror CC.

third_party/WebKit/Source/core/frame/FrameView.h

 /*
    Copyright (C) 1997 Martin Jones (mjones@kde.org)
              (C) 1998 Waldo Bastian (bastian@kde.org)
              (C) 1998, 1999 Torben Weis (weis@kde.org)
              (C) 1999 Lars Knoll (knoll@kde.org)
              (C) 1999 Antti Koivisto (koivisto@kde.org)
    Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. 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 338 matching lines @@
         m_tickmarks = tickmarks;
         invalidatePaintForTickmarks();
     }
 
     void invalidatePaintForTickmarks();
 
     // Since the compositor can resize the viewport due to top controls and
     // commit scroll offsets before a WebView::resize occurs, we need to adjust
     // our scroll extents to prevent clamping the scroll offsets.
     void setTopControlsViewportAdjustment(float);
-    IntSize topControlsSize() const { return IntSize(0, roundf(m_topControlsViewportAdjustment)); }
+    IntSize topControlsSize() const { return IntSize(0, ceilf(m_topControlsViewportAdjustment)); }
 
     IntPoint maximumScrollPosition() const override;
 
     // ScrollableArea interface
     void scrollControlWasSetNeedsPaintInvalidation() override { }
     void getTickmarks(Vector<IntRect>&) const override;
     IntRect scrollableAreaBoundingBox() const override;
     bool scrollAnimatorEnabled() const override;
     bool usesCompositedScrolling() const override;
     bool shouldScrollOnMainThread() const override;
@@ skipping 558 matching lines @@
     if (m_visuallyNonEmptyPixelCount > visualPixelThreshold)
         setIsVisuallyNonEmpty();
 }
 
 DEFINE_TYPE_CASTS(FrameView, Widget, widget, widget->isFrameView(), widget.isFrameView());
 DEFINE_TYPE_CASTS(FrameView, ScrollableArea, scrollableArea, scrollableArea->isFrameView(), scrollableArea.isFrameView());
 
 } // namespace blink
 
 #endif // FrameView_h