ViewPainter should skip background in print economy mode

Source/core/paint/ViewPainter.cpp

Index: Source/core/paint/ViewPainter.cpp
diff --git a/Source/core/paint/ViewPainter.cpp b/Source/core/paint/ViewPainter.cpp
index fd892d571a52e8ebc3a2a99f43c804adeaff4f20..b67f1471e100fe1feccf04f78c842c64c91a3720 100644
--- a/Source/core/paint/ViewPainter.cpp
+++ b/Source/core/paint/ViewPainter.cpp
@@ -56,12 +56,22 @@ void ViewPainter::paintBoxDecorationBackground(const PaintInfo& paintInfo)
     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.
+    if (document.printing() && m_layoutView.style()->printColorAdjust() == PrintColorAdjustEconomy

[chrishtr, 2015/06/23 17:42:57]

Where did this logic used to be before your refactor?

[trchen, 2015/06/23 20:40:15]

https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

This new code should be equivalent if I didn't make any logical fallacy. :3

+        && (!document.settings() || !document.settings()->shouldPrintBackgrounds())) {
+        // 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.
@@ -100,7 +110,6 @@ void ViewPainter::paintBoxDecorationBackground(const PaintInfo& paintInfo)
     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.