Expose a way to set a view's base background color.

Source/core/page/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 2023 matching lines @@
     return m_baseBackgroundColor;
 }
 
 void FrameView::setBaseBackgroundColor(const Color& backgroundColor)
 {
     if (!backgroundColor.isValid())
         m_baseBackgroundColor = Color::white;
     else
         m_baseBackgroundColor = backgroundColor;
 
-    if (renderView() && renderView()->layer()->backing())
-        renderView()->layer()->backing()->updateContentsOpaque();
+    if (RenderLayerBacking* backing = renderView() ? renderView()->layer()->backing() : 0) {
+        backing->updateContentsOpaque();
+        if (backing->graphicsLayer())
+            backing->graphicsLayer()->setNeedsDisplay();
+    }
     recalculateScrollbarOverlayStyle();
 }
 
 void FrameView::updateBackgroundRecursively(const Color& backgroundColor, bool transparent)
 {
     for (Frame* frame = m_frame.get(); frame; frame = frame->tree()->traverseNext(m_frame.get())) {
         if (FrameView* view = frame->view()) {
             view->setTransparent(transparent);
             view->setBaseBackgroundColor(backgroundColor);
         }
@@ skipping 1317 matching lines @@
 }
 
 AXObjectCache* FrameView::axObjectCache() const
 {
     if (frame() && frame()->document())
         return frame()->document()->existingAXObjectCache();
     return 0;
 }
 
 } // namespace WebCore