Linux UI: Dynamically respond to changes in the scale factor

ui/views/linux_ui/linux_ui.h

Index: ui/views/linux_ui/linux_ui.h
diff --git a/ui/views/linux_ui/linux_ui.h b/ui/views/linux_ui/linux_ui.h
index b7de506d154cef0015010274ee4a675fad21ed22..bc831d80f8f952f4895cb52d36f90edfb6baf123 100644
--- a/ui/views/linux_ui/linux_ui.h
+++ b/ui/views/linux_ui/linux_ui.h
@@ -38,6 +38,7 @@ class NativeTheme;
 
 namespace views {
 class Border;
+class DeviceScaleFactorObserver;
 class LabelButton;
 class LabelButtonBorder;
 class WindowButtonOrderObserver;
@@ -157,6 +158,16 @@ class VIEWS_EXPORT LinuxUI : public ui::LinuxInputMethodContextFactory,
 
   // Determines the device scale factor of the primary screen.
   virtual float GetDeviceScaleFactor() const = 0;
+
+  // Registers |observer| to be notified about changes to the device
+  // scale factor.
+  virtual void AddDeviceScaleFactorObserver(
+      DeviceScaleFactorObserver* observer) = 0;
+
+  // Unregisters |observer| from receiving changes to the device scale
+  // factor.
+  virtual void RemoveDeviceScaleFactorObserver(
+      DeviceScaleFactorObserver* observer) = 0;
 };
 
 }  // namespace views