Pass device scale factor from display to ws.

services/ui/ws/platform_display_delegate.h

Index: services/ui/ws/platform_display_delegate.h
diff --git a/services/ui/ws/platform_display_delegate.h b/services/ui/ws/platform_display_delegate.h
index 7daf17da384388c6c2d3dfd05f2b95349ece3cfb..f027ba4711150b36d6f2d33a2b09f7bc9be2b07f 100644
--- a/services/ui/ws/platform_display_delegate.h
+++ b/services/ui/ws/platform_display_delegate.h
@@ -7,6 +7,10 @@
 
 #include "services/ui/ws/ids.h"
 
+namespace gfx {
+class Size;
+}
+
 namespace ui {
 class Event;
 }
@@ -23,6 +27,9 @@ struct ViewportMetrics;
 /// and responses to changes in viewport size.
 class PlatformDisplayDelegate {
  public:
+  // Creates the root window for this display with |size|.
+  virtual void CreateRootWindow(const gfx::Size& size);

[sky, 2016/09/22 21:42:06]

Naming this CreateRootWindow() is rather specific to what the implementation
does. Isn't this more of something like Init(size)? Also, it's worth clarifying
what units size is in.

[kylechar, 2016/09/23 13:22:32]

I've added the units for size. Unfortunately there is already a Display::Init()
method that does something else which depends on the root ServerWindow existing.

In general though, the creation of Display/PlatformDisplay could be simplified
with a bit of work.

+
   // Returns the root window of this display.
   virtual ServerWindow* GetRootWindow() = 0;