Pass device scale factor from display to ws.

services/ui/ws/platform_display_delegate.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef SERVICES_UI_WS_PLATFORM_DISPLAY_DELEGATE_H_
 #define SERVICES_UI_WS_PLATFORM_DISPLAY_DELEGATE_H_
 
 #include "services/ui/ws/ids.h"
 
+namespace gfx {
+class Size;
+}
+
 namespace ui {
 class Event;
 }
 
 namespace ui {
 
 namespace ws {
 
 class ServerWindow;
 struct ViewportMetrics;
 
 // PlatformDisplayDelegate is implemented by an object that manages the
 // lifetime of a PlatformDisplay, forwards events to the appropriate windows,
 /// 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;
 
   virtual bool IsInHighContrastMode() = 0;
 
   // Called when an event arrives.
   virtual void OnEvent(const ui::Event& event) = 0;
 
   // Called when the Display loses capture.
   virtual void OnNativeCaptureLost() = 0;
 
   // Signals that the metrics of this display's viewport has changed.
   virtual void OnViewportMetricsChanged(const ViewportMetrics& old_metrics,
                                         const ViewportMetrics& new_metrics) = 0;
 
   // Called when a compositor frame is finished drawing.
   virtual void OnCompositorFrameDrawn() = 0;
 
  protected:
   virtual ~PlatformDisplayDelegate() {}
 };
 
 }  // namespace ws
 
 }  // namespace ui
 
 #endif  // SERVICES_UI_WS_PLATFORM_DISPLAY_DELEGATE_H_