Resize background-attachment: fixed when inertTopControls is enabled.

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 1465 matching lines @@
     // 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).
     LayoutViewItem lvi = layoutViewItem();
     if (!lvi.isNull())
       lvi.setShouldDoFullPaintInvalidation();
   }
 
+  if (RuntimeEnabledFeatures::inertTopControlsEnabled() && layoutView() &&
+      layoutView()->style()->hasFixedBackgroundImage()) {
+    // In the case where we don't change layout size from top control resizes,
+    // we wont perform a layout. If we have a fixed background image however,
+    // the background layer needs to get resized so we should request a layout
+    // explicitly.
+    PaintLayer* layer = layoutView()->layer();
+    if (layoutView()->compositor()->needsFixedRootBackgroundLayer(layer)) {
+      setNeedsLayout();
+    } else if (!RuntimeEnabledFeatures::rootLayerScrollingEnabled()) {
+      // If root layer scrolls if on, we've already issued a full invalidation

[flackr, 2016/10/31 18:17:55]

nit s/if on/is on

[bokan, 2016/11/01 20:27:58]

Done.

+      // above.
+      layoutView()->setShouldDoFullPaintInvalidationOnResizeIfNeeded(
+          widthChanged, heightChanged);
+    }
+  }
+
   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();
@@ skipping 3044 matching lines @@
   DCHECK(m_frame->isMainFrame());
   return m_initialViewportSize.width();
 }
 
 int FrameView::initialViewportHeight() const {
   DCHECK(m_frame->isMainFrame());
   return m_initialViewportSize.height();
 }
 
 }  // namespace blink