Linux UI: Dynamically respond to changes in the scale factor

ui/views/widget/desktop_aura/desktop_screen_x11.h

 // Copyright (c) 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_WIDGET_DESKTOP_AURA_DESKTOP_SCREEN_X11_H_
 #define UI_VIEWS_WIDGET_DESKTOP_AURA_DESKTOP_SCREEN_X11_H_
 
 #include <stdint.h>
 
 #include <memory>
 
+#include "base/cancelable_callback.h"
 #include "base/macros.h"
-#include "base/timer/timer.h"
 #include "ui/display/display_change_notifier.h"
 #include "ui/display/screen.h"
 #include "ui/events/platform/platform_event_dispatcher.h"
+#include "ui/views/linux_ui/device_scale_factor_observer.h"
 #include "ui/views/views_export.h"
 
 typedef unsigned long XID;
 typedef XID Window;
 typedef struct _XDisplay Display;
 
 namespace views {
 class DesktopScreenX11Test;
 
 namespace test {
 class DesktopScreenX11TestApi;
 }
 
 // Our singleton screen implementation that talks to xrandr.
 class VIEWS_EXPORT DesktopScreenX11 : public display::Screen,
-                                      public ui::PlatformEventDispatcher {
+                                      public ui::PlatformEventDispatcher,
+                                      public views::DeviceScaleFactorObserver {
  public:
   DesktopScreenX11();
 
   ~DesktopScreenX11() override;
 
   // Overridden from display::Screen:
   gfx::Point GetCursorScreenPoint() override;
   bool IsWindowUnderCursor(gfx::NativeWindow window) override;
   gfx::NativeWindow GetWindowAtScreenPoint(const gfx::Point& point) override;
   int GetNumDisplays() const override;
   const std::vector<display::Display>& GetAllDisplays() const override;
   display::Display GetDisplayNearestWindow(
       gfx::NativeView window) const override;
   display::Display GetDisplayNearestPoint(
       const gfx::Point& point) const override;
   display::Display GetDisplayMatching(
       const gfx::Rect& match_rect) const override;
   display::Display GetPrimaryDisplay() const override;
   void AddObserver(display::DisplayObserver* observer) override;
   void RemoveObserver(display::DisplayObserver* observer) override;
 
   // ui::PlatformEventDispatcher:
   bool CanDispatchEvent(const ui::PlatformEvent& event) override;
   uint32_t DispatchEvent(const ui::PlatformEvent& event) override;
 
+  // views::DeviceScaleFactorObserver:
+  void OnDeviceScaleFactorChanged() override;
+
   static void UpdateDeviceScaleFactorForTest();
 
  private:
   friend class DesktopScreenX11Test;
   friend class test::DesktopScreenX11TestApi;
 
   // Constructor used in tests.
   DesktopScreenX11(const std::vector<display::Display>& test_displays);
 
   // Builds a list of displays from the current screen information offered by
   // the X server.
   std::vector<display::Display> BuildDisplaysFromXRandRInfo();
 
-  // We delay updating the display so we can coalesce events.
-  void ConfigureTimerFired();
+  // Removes |delayed_configuration_task_| from the task queue (if
+  // it's in the queue) and adds it back at the end of the queue.
+  void RestartDelayedConfigurationTask();
 
-  // Updates |displays_| and sets FontRenderParams's scale factor.
+  // Updates |displays_| with the latest XRandR info.
+  void UpdateDisplays();
+
+  // Updates |displays_| from |displays| and sets FontRenderParams's scale
+  // factor.
   void SetDisplaysInternal(const std::vector<display::Display>& displays);
 
   Display* xdisplay_;
   ::Window x_root_window_;
 
   // Whether the x server supports the XRandR extension.
   bool has_xrandr_;
 
   // The base of the event numbers used to represent XRandr events used in
   // decoding events regarding output add/remove.
   int xrandr_event_base_;
 
   // The display objects we present to chrome.
   std::vector<display::Display> displays_;
 
   // The index into displays_ that represents the primary display.
   size_t primary_display_index_;
 
-  // The timer to delay configuring outputs. See also the comments in
-  // Dispatch().
-  std::unique_ptr<base::OneShotTimer> configure_timer_;
+  // The task to delay configuring outputs.  We delay updating the
+  // display so we can coalesce events.
+  base::CancelableCallback<void()> delayed_configuration_task_;
 
   display::DisplayChangeNotifier change_notifier_;
 
+  base::WeakPtrFactory<DesktopScreenX11> weak_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(DesktopScreenX11);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_WIDGET_DESKTOP_AURA_DESKTOP_SCREEN_X11_H_