Make exo::Surface set device_scale_factor.

components/exo/surface.h

Index: components/exo/surface.h
diff --git a/components/exo/surface.h b/components/exo/surface.h
index 1b1bd552623de0bdefb180100391de83e7f5d2b9..c22029d32f8fff7eb5123ec2d6cb49e2d4a41a9a 100644
--- a/components/exo/surface.h
+++ b/components/exo/surface.h
@@ -140,6 +140,9 @@ class Surface : public ui::ContextFactoryObserver,
   // This sets the alpha value that will be applied to the whole surface.
   void SetAlpha(float alpha);
 
+  // This sets the device scale factor sent in CompositorFrames.
+  void SetDeviceScaleFactor(float device_scale_factor);
+
   // Surface state (damage regions, attached buffers, etc.) is double-buffered.
   // A Commit() call atomically applies all pending state, replacing the
   // current state. Commit() is not guaranteed to be synchronous. See
@@ -314,6 +317,9 @@ class Surface : public ui::ContextFactoryObserver,
   // The buffer that will become the content of surface when Commit() is called.
   BufferAttachment pending_buffer_;
 
+  // The device scale factor sent in CompositorFrames.
+  float device_scale_factor_ = 1.0f;

[reveman, 2017/04/27 21:01:30]

Did you verify that this is updated as the |windiow_| is added to the window
hierarchy?

[kylechar, 2017/04/28 18:02:16]

It gets updated when the ui::Layer with |window_| as it's delegate gets added to
the LayerTree. It looks like UpdateSurface() can get called once or twice before
that happens, but since the ui::Layer isn't in the tree yet I don't think those
CompositorFrames would be embedded anywhere?

Does exo use ui::SurfaceLayers to embed content or is something special going on
with those fullscreen exo::Surfaces?

[reveman, 2017/04/28 18:06:49]

Sounds good. UpdateSurface calls before delegate is added to the tree should not
produce any contents so we should be fine.
We always use ui::SurfaceLayers afaik.

+
   const cc::FrameSinkId frame_sink_id_;
   cc::LocalSurfaceId local_surface_id_;