Call the correct superclass in RenderSlider

The superclass is RenderFlexibleBox, not RenderBlock.

No visual change.

R=ojan@chromium.org
BUG=

Review URL: https://codereview.chromium.org/13747002

git-svn-id: svn://svn.chromium.org/blink/trunk@147850 bbb929c8-8fbe-4397-9dbb-9b2b20218538
diff --git a/Source/WebCore/rendering/RenderSlider.cpp b/Source/WebCore/rendering/RenderSlider.cpp
index e53f8e5..2f38165 100644
--- a/Source/WebCore/rendering/RenderSlider.cpp
+++ b/Source/WebCore/rendering/RenderSlider.cpp
@@ -113,7 +113,7 @@
     if (thumbBox && thumbBox->isSliderThumb())
         static_cast<RenderSliderThumb*>(thumbBox)->updateAppearance(style());
 
-    RenderBlock::layout();
+    RenderFlexibleBox::layout();
 }
 
 bool RenderSlider::inDragMode() const