Merge 147127 "RenderBox::backgroundIsKnownToBeOpaqueInRect may b..."

Source/WebCore/rendering/RenderBox.cpp

Index: Source/WebCore/rendering/RenderBox.cpp
===================================================================
--- Source/WebCore/rendering/RenderBox.cpp	(revision 147447)
+++ Source/WebCore/rendering/RenderBox.cpp	(working copy)
@@ -1171,6 +1171,12 @@
     if (!backgroundColor.isValid() || backgroundColor.hasAlpha())
         return false;
 
+    // If the element has appearance, it might be painted by theme.
+    // We cannot be sure if theme paints the background opaque.
+    // In this case it is safe to not assume opaqueness.
+    // FIXME: May be ask theme if it paints opaque.
+    if (style()->hasAppearance())
+        return false;
     // FIXME: Check the opaqueness of background images.
 
     // FIXME: Use rounded rect if border radius is present.