Pass device scale factor from display to ws.

services/ui/display/platform_screen_delegate.h

Index: services/ui/display/platform_screen_delegate.h
diff --git a/services/ui/display/platform_screen_delegate.h b/services/ui/display/platform_screen_delegate.h
index 9c0e144a37778991d893b045047c09a01d381cd5..24899359990f06a8194ee28463b344e57e2e2013 100644
--- a/services/ui/display/platform_screen_delegate.h
+++ b/services/ui/display/platform_screen_delegate.h
@@ -9,6 +9,7 @@
 
 namespace gfx {
 class Rect;
+class Size;
 }
 
 namespace display {
@@ -19,17 +20,25 @@ class PlatformScreen;
 // and/or virtual displays by PlatformScreen.
 class PlatformScreenDelegate {
  public:
-  // TODO(kylechar): We need to provide more than just the window bounds when
-  // displays are added or modified.
-
-  // Called when a display is added. |bounds| is in DIP.
-  virtual void OnDisplayAdded(int64_t id, const gfx::Rect& bounds) = 0;
-
-  // Called when a display is removed.
+  // Called when a display is added. |id| is the display id for the new display,
+  // |bounds| is the display origin and size in DIP, |pixel_size| is the size
+  // of the display in DDP and |device_scale_factor| is the output device pixel
+  // scale factor.
+  virtual void OnDisplayAdded(int64_t id,
+                              const gfx::Rect& bounds,
+                              const gfx::Size& pixel_size,
+                              float device_scale_factor) = 0;

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

Do you need to specify if the new display is the primary? Same thing with
OnDisplayModified, might it become the primary?

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

PlatformDisplay queries PlatformScreen to check if it's the primary display.
That info gets included in the mojom::WsDisplay that ws::DisplayManager sends
when a display is added/removed/modified. So everything should work fine when a
display is added at least.

Changing the primary display won't really work though. I'll go through that code
path and check it works when I finish ws::DisplayManager::OnDisplayModified()
next. That will require a couple of changes I think.

+
+  // Called when a display is removed. |id| is the display id for the display
+  // that was removed.
   virtual void OnDisplayRemoved(int64_t id) = 0;
 
-  // Called when a display is modified. |bounds| is in DIP.
-  virtual void OnDisplayModified(int64_t id, const gfx::Rect& bounds) = 0;
+  // Called when a display is modified. See |OnDisplayAdded| for parameter

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

Generally we use params for function calls rather than |'s, e.g.,
OnDisplayAdded() rather than |OnDisplayAdded|.

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

Done.

+  // information.
+  virtual void OnDisplayModified(int64_t id,
+                                 const gfx::Rect& bounds,
+                                 const gfx::Size& pixel_size,
+                                 float device_scale_factor) = 0;
 
  protected:
   virtual ~PlatformScreenDelegate() {}