NOT FOR COMMIT: sample CL to debug white flashes.

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

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/paint/ViewPainter.h"
 
 #include "core/frame/FrameView.h"
 #include "core/frame/Settings.h"
 #include "core/layout/LayoutBox.h"
 #include "core/layout/LayoutView.h"
@@ skipping 111 matching lines @@
     if (!baseBackgroundColor.alpha() && shouldClearCanvas)
         shouldDrawBackgroundInSeparateBuffer = false;
 
     if (shouldDrawBackgroundInSeparateBuffer) {
         if (baseBackgroundColor.alpha())
             context.fillRect(backgroundRect, baseBackgroundColor, shouldClearCanvas ? SkXfermode::kSrc_Mode : SkXfermode::kSrcOver_Mode);
         context.beginLayer();
     }
 
     Color combinedBackgroundColor = shouldDrawBackgroundInSeparateBuffer ? rootBackgroundColor : baseBackgroundColor.blend(rootBackgroundColor);
+    LOG(ERROR) << "Document background color: " << combinedBackgroundColor.serialized();
     if (combinedBackgroundColor.alpha()) {
         if (!combinedBackgroundColor.hasAlpha() && RuntimeEnabledFeatures::slimmingPaintV2Enabled())
             recorder.setKnownToBeOpaque();
         context.fillRect(backgroundRect, combinedBackgroundColor, (shouldDrawBackgroundInSeparateBuffer || shouldClearCanvas) ? SkXfermode::kSrc_Mode : SkXfermode::kSrcOver_Mode);
     } else if (shouldClearCanvas && !shouldDrawBackgroundInSeparateBuffer) {
         context.fillRect(backgroundRect, Color(), SkXfermode::kClear_Mode);
     }
 
     for (auto it = reversedPaintList.rbegin(); it != reversedPaintList.rend(); ++it) {
         ASSERT((*it)->clip() == BorderFillBox);
 
         bool shouldPaintInViewportSpace = (*it)->attachment() == FixedBackgroundAttachment;
         if (shouldPaintInViewportSpace) {
             BoxPainter::paintFillLayer(m_layoutView, paintInfo, Color(), **it, LayoutRect(LayoutRect::infiniteIntRect()), BackgroundBleedNone);
         } else {
             context.save();
             // TODO(trchen): We should be able to handle 3D-transformed root
             // background with slimming paint by using transform display items.
             context.concatCTM(transform.toAffineTransform());
             BoxPainter::paintFillLayer(m_layoutView, paintInfo, Color(), **it, LayoutRect(paintRect), BackgroundBleedNone);
             context.restore();
         }
     }
 
     if (shouldDrawBackgroundInSeparateBuffer)
         context.endLayer();
 }
 
 } // namespace blink