ViewPainter should skip background in print economy mode

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 "config.h"
 #include "core/paint/ViewPainter.h"
 
 #include "core/frame/FrameView.h"
 #include "core/frame/Settings.h"
 #include "core/layout/LayoutBox.h"
@@ skipping 38 matching lines @@
     //    culling and pre-blending optimization when possible.
 
     GraphicsContext& context = *paintInfo.context;
     IntRect documentRect = m_layoutView.unscaledDocumentRect();
     const Document& document = m_layoutView.document();
     const FrameView& frameView = *m_layoutView.frameView();
     bool isMainFrame = !document.ownerElement();
     bool paintsBaseBackground = isMainFrame && !frameView.isTransparent();
     bool shouldClearCanvas = paintsBaseBackground && (document.settings() && document.settings()->shouldClearDocumentBackground());
     Color baseBackgroundColor = paintsBaseBackground ? frameView.baseBackgroundColor() : Color();
+    Color rootBackgroundColor = m_layoutView.style()->visitedDependentColor(CSSPropertyBackgroundColor);
     const LayoutObject* rootObject = document.documentElement() ? document.documentElement()->layoutObject() : nullptr;
 
     LayoutObjectDrawingRecorder recorder(context, m_layoutView, DisplayItem::BoxDecorationBackground, documentRect);
     if (recorder.canUseCachedDrawing())
         return;
 
+    // Special handling for print economy mode.
+    bool forceBackgroundToWhite = BoxPainter::shouldForceWhiteBackgroundForPrintEconomy(m_layoutView.styleRef(), document);
+    if (forceBackgroundToWhite) {
+        // If for any reason the view background is not transparent, paint white instead, otherwise keep transparent as is.
+        if (paintsBaseBackground || rootBackgroundColor.alpha() || m_layoutView.style()->backgroundLayers().image())
+            context.fillRect(documentRect, Color::white, SkXfermode::kSrc_Mode);
+        return;
+    }
+
     // Compute the enclosing rect of the view, in root element space.
     //
     // For background colors we can simply paint the document rect in the default space.
     // However for background image, the root element transform applies. The strategy is to apply
     // root element transform on the context and issue draw commands in the local space, therefore
     // we need to apply inverse transform on the document rect to get to the root element space.
     bool backgroundRenderable = true;
     TransformationMatrix transform;
     IntRect paintRect = documentRect;
     if (!rootObject || !rootObject->isBox()) {
@@ skipping 18 matching lines @@
         if (baseBackgroundColor.alpha())
             context.fillRect(documentRect, baseBackgroundColor, shouldClearCanvas ? SkXfermode::kSrc_Mode : SkXfermode::kSrcOver_Mode);
         else if (shouldClearCanvas)
             context.fillRect(documentRect, Color(), SkXfermode::kClear_Mode);
         return;
     }
 
     BoxPainter::FillLayerOcclusionOutputList reversedPaintList;
     bool shouldDrawBackgroundInSeparateBuffer = BoxPainter(m_layoutView).calculateFillLayerOcclusionCulling(reversedPaintList, m_layoutView.style()->backgroundLayers());
     ASSERT(reversedPaintList.size());
-    Color rootBackgroundColor = m_layoutView.style()->visitedDependentColor(CSSPropertyBackgroundColor);
 
     // If the root background color is opaque, isolation group can be skipped because the canvas
     // will be cleared by root background color.
     if (!rootBackgroundColor.hasAlpha())
         shouldDrawBackgroundInSeparateBuffer = false;
 
     // We are going to clear the canvas with transparent pixels, isolation group can be skipped.
     if (!baseBackgroundColor.alpha() && shouldClearCanvas)
         shouldDrawBackgroundInSeparateBuffer = false;
 
@@ skipping 17 matching lines @@
         ASSERT((*it)->clip() == BorderFillBox);
         BoxPainter::paintFillLayerExtended(m_layoutView, paintInfo, Color(), **it, LayoutRect(paintRect), BackgroundBleedNone);
     }
     context.restore();
 
     if (shouldDrawBackgroundInSeparateBuffer)
         context.endLayer();
 }
 
 } // namespace blink