Linux UI: Dynamically respond to changes in the scale factor

ui/views/linux_ui/linux_ui.h

 // Copyright 2013 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 UI_VIEWS_LINUX_UI_LINUX_UI_H_
 #define UI_VIEWS_LINUX_UI_LINUX_UI_H_
 
 #include <string>
 
 #include "base/callback.h"
@@ skipping 20 matching lines @@
 namespace gfx {
 class Image;
 }
 
 namespace ui {
 class NativeTheme;
 }
 
 namespace views {
 class Border;
+class DeviceScaleFactorObserver;
 class LabelButton;
 class LabelButtonBorder;
 class WindowButtonOrderObserver;
 
 // Adapter class with targets to render like different toolkits. Set by any
 // project that wants to do linux desktop native rendering.
 //
 // TODO(erg): We're hardcoding GTK2, when we'll need to have backends for (at
 // minimum) GTK2 and GTK3. LinuxUI::instance() should actually be a very
 // complex method that pokes around with dlopen against a libuigtk2.so, a
@@ skipping 99 matching lines @@
   // automatically. In case Chromium does not open a new window on startup,
   // e.g. an existing browser window already exists, this should be called.
   virtual void NotifyWindowManagerStartupComplete() = 0;
 
   // Updates the device scale factor so that the default font size can be
   // recalculated.
   virtual void UpdateDeviceScaleFactor() = 0;
 
   // 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
 
 #endif  // UI_VIEWS_LINUX_UI_LINUX_UI_H_