Refactor root element background painting

Source/core/style/FillLayer.cpp

Index: Source/core/style/FillLayer.cpp
diff --git a/Source/core/style/FillLayer.cpp b/Source/core/style/FillLayer.cpp
index d5b9ff901f9ffd3c839e045f5afa9de9267bfbd9..a031ddf9d06a726556c513c808bf121f2a71ee91 100644
--- a/Source/core/style/FillLayer.cpp
+++ b/Source/core/style/FillLayer.cpp
@@ -368,12 +368,15 @@ bool FillLayer::hasOpaqueImage(const LayoutObject* layoutObject) const
     if (!m_image)
         return false;
 
-    if (m_composite == CompositeClear || m_composite == CompositeCopy)
+    if (m_composite == CompositeClear)
         return true;
 
     if (m_blendMode != WebBlendModeNormal)
         return false;
 
+    if (m_composite == CompositeCopy)

[chrishtr, 2015/06/09 21:07:54]

Why this change?

[trchen, 2015/06/09 23:36:08]

Not necessary in this CL. Just fix it on the way when I saw it.

Blending is applied before compositing. Non-default blending with composite:copy
means first absorbing color from below, then discard the layer below, thus not
really being opaque.

[chrishtr, 2015/06/10 01:03:39]

Ok please move into another patch then.

[trchen, 2015/06/10 01:41:05]

Done.

+        return true;
+
     if (m_composite == CompositeSourceOver)
         return m_image->knownToBeOpaque(layoutObject);