DNS: Testing for [blink] Support (semi-)transparent background colors.

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 68 matching lines @@
                            m_layoutView.scrolledContentOffset());
   }
 
   if (DrawingRecorder::useCachedDrawingIfPossible(
           context, *displayItemClient, DisplayItem::kDocumentBackground))
     return;
 
   const Document& document = m_layoutView.document();
   const FrameView& frameView = *m_layoutView.frameView();
   bool isMainFrame = document.isInMainFrame();
-  bool paintsBaseBackground = isMainFrame && !frameView.isTransparent();
+  bool paintsBaseBackground =
+      isMainFrame && !frameView.baseBackgroundColor().hasAlpha();
   bool shouldClearCanvas =
       paintsBaseBackground &&
       (document.settings() &&
        document.settings()->getShouldClearDocumentBackground());
   Color baseBackgroundColor =
       paintsBaseBackground ? frameView.baseBackgroundColor() : Color();
   Color rootBackgroundColor =
       m_layoutView.style()->visitedDependentColor(CSSPropertyBackgroundColor);
   const LayoutObject* rootObject =
       document.documentElement() ? document.documentElement()->layoutObject()
@@ skipping 123 matching lines @@
                                  LayoutRect(paintRect), BackgroundBleedNone);
       context.restore();
     }
   }
 
   if (shouldDrawBackgroundInSeparateBuffer)
     context.endLayer();
 }
 
 }  // namespace blink