Invalidate LayoutView when the URL bar is hidden on short pages.

third_party/WebKit/Source/core/layout/LayoutView.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@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
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 211 matching lines @@
   }
 }
 
 void LayoutView::layout() {
   if (!document().paginated())
     setPageLogicalHeight(LayoutUnit());
 
   IncludeScrollbarsInRect includeScrollbars =
       RuntimeEnabledFeatures::rootLayerScrollingEnabled() ? IncludeScrollbars
                                                           : ExcludeScrollbars;
-  FloatSize viewSize(frameView()->visibleContentSize(includeScrollbars));
   setShouldDoFullPaintInvalidationOnResizeIfNeeded(
-      offsetWidth() != viewSize.width(), offsetHeight() != viewSize.height());
+      offsetWidth() != layoutSize(includeScrollbars).width(),

[bokan, 2016/12/22 00:45:49]

In https://codereview.chromium.org/2461463004, I moved these
`widthChanged`|`heightChanged` calculations from
setShouldDoFullPaintInvalidationOnResizeIfNeeded to the call sites and passed
them as parameters. I made a mistake though in that I assumed
viewWidth|viewHeight == visibleContentSize -- they are not. viewWidth|viewHeight
are actually layoutWidth and layoutHeight. The mistake wasn't caught because it
was masked by the invalidation that happens in FrameView::viewportSizeChanged.
Now that I've tightened that up to happen only when there's a mobile URL bar it
caused window-resize-background-image-generated|fixed.html to fail.

+      offsetHeight() != layoutSize(includeScrollbars).height());
 
   if (pageLogicalHeight() && shouldUsePrintingLayout()) {
     m_minPreferredLogicalWidth = m_maxPreferredLogicalWidth = logicalWidth();
     if (!m_fragmentationContext) {
       m_fragmentationContext =
           WTF::wrapUnique(new ViewFragmentationContext(*this));
       m_paginationStateChanged = true;
     }
   } else if (m_fragmentationContext) {
     m_fragmentationContext.reset();
@@ skipping 786 matching lines @@
 bool LayoutView::paintedOutputOfObjectHasNoEffectRegardlessOfSize() const {
   // Frame scroll corner is painted using LayoutView as the display item client.
   if (!RuntimeEnabledFeatures::rootLayerScrollingEnabled() &&
       (frameView()->horizontalScrollbar() || frameView()->verticalScrollbar()))
     return false;
 
   return LayoutBlockFlow::paintedOutputOfObjectHasNoEffectRegardlessOfSize();
 }
 
 }  // namespace blink