Explicitly specify contents scale for SurfaceLayer.

ui/compositor/layer.cc

Index: ui/compositor/layer.cc
diff --git a/ui/compositor/layer.cc b/ui/compositor/layer.cc
index 5f8800dc79f5d32accaea34f6c09c3a42230d608..d3d56348ebe49afbe39166534b08bb2323d1b13b 100644
--- a/ui/compositor/layer.cc
+++ b/ui/compositor/layer.cc
@@ -579,7 +579,11 @@ void Layer::SetShowSurface(
 
   scoped_refptr<cc::SurfaceLayer> new_layer =
       cc::SurfaceLayer::Create(satisfy_callback, require_callback);
-  new_layer->SetSurfaceId(surface_id, surface_size);
+  float scale =
+      frame_size_in_dip.width() > 0
+          ? static_cast<float>(surface_size.width()) / frame_size_in_dip.width()
+          : 1.f;

[piman, 2014/11/12 02:36:57]

Any reason we're not passing the renderer's DSF instead of recomputing it?

In the caller, frame_size_in_dip is computed explicitly from the frame_size
(surface_size) and the renderer's DSF. It seems it would avoid additional
precision issues for non-pow2 DSF.

+  new_layer->SetSurfaceId(surface_id, scale, surface_size);
   SwitchToLayer(new_layer);
   surface_layer_ = new_layer;