Pass accurate contentsScale to LayerImpl.

cc/scrollbar_layer.cc

Index: cc/scrollbar_layer.cc
diff --git a/cc/scrollbar_layer.cc b/cc/scrollbar_layer.cc
index 1a107bd810ef9b4d50c844266016a588d0882b2f..50c06a1d84dda1f5a7d26693a9ede7c4235b32b4 100644
--- a/cc/scrollbar_layer.cc
+++ b/cc/scrollbar_layer.cc
@@ -43,7 +43,7 @@ ScrollbarLayer::~ScrollbarLayer()
 
 void ScrollbarLayer::pushPropertiesTo(LayerImpl* layer)
 {
-    Layer::pushPropertiesTo(layer);
+    ContentsScalingLayer::pushPropertiesTo(layer);
 
     ScrollbarLayerImpl* scrollbarLayer = static_cast<ScrollbarLayerImpl*>(layer);
 
@@ -131,16 +131,6 @@ private:
     DISALLOW_COPY_AND_ASSIGN(ScrollbarBackgroundPainter);
 };
 
-bool ScrollbarLayer::needsContentsScale() const
-{
-    return true;
-}
-
-IntSize ScrollbarLayer::contentBounds() const
-{
-    return IntSize(lroundf(bounds().width() * contentsScale()), lroundf(bounds().height() * contentsScale()));
-}
-
 class ScrollbarThumbPainter : public LayerPainter {
 public:
     static scoped_ptr<ScrollbarThumbPainter> create(WebKit::WebScrollbar* scrollbar, WebKit::WebScrollbarThemePainter painter, WebKit::WebScrollbarThemeGeometry* geometry)
@@ -183,7 +173,7 @@ void ScrollbarLayer::setLayerTreeHost(LayerTreeHost* host)
         m_thumb.reset();
     }
 
-    Layer::setLayerTreeHost(host);
+    ContentsScalingLayer::setLayerTreeHost(host);
 }
 
 void ScrollbarLayer::createUpdaterIfNeeded()
@@ -224,10 +214,8 @@ void ScrollbarLayer::updatePart(CachingBitmapContentLayerUpdater* painter, Layer
         return;
 
     // Paint and upload the entire part.
-    float widthScale = static_cast<float>(contentBounds().width()) / bounds().width();
-    float heightScale = static_cast<float>(contentBounds().height()) / bounds().height();
     IntRect paintedOpaqueRect;
-    painter->prepareToUpdate(rect, rect.size(), widthScale, heightScale, paintedOpaqueRect, stats);
+    painter->prepareToUpdate(rect, rect.size(), contentsScaleX(), contentsScaleY(), paintedOpaqueRect, stats);
     if (!painter->pixelsDidChange() && texture->texture()->haveBackingTexture()) {
         TRACE_EVENT_INSTANT0("cc","ScrollbarLayer::updatePart no texture upload needed");
         return;