Linux UI: Dynamically respond to changes in the scale factor

ui/views/widget/desktop_aura/desktop_screen_x11.h

Index: ui/views/widget/desktop_aura/desktop_screen_x11.h
diff --git a/ui/views/widget/desktop_aura/desktop_screen_x11.h b/ui/views/widget/desktop_aura/desktop_screen_x11.h
index fc71915321abb156526479b7c7ed48ce6341d7eb..91a85ce6fda6ab8c28293d886c2a314b63a5dd28 100644
--- a/ui/views/widget/desktop_aura/desktop_screen_x11.h
+++ b/ui/views/widget/desktop_aura/desktop_screen_x11.h
@@ -9,11 +9,12 @@
 
 #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;
@@ -29,7 +30,8 @@ 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();
 
@@ -55,6 +57,9 @@ class VIEWS_EXPORT DesktopScreenX11 : public display::Screen,
   bool CanDispatchEvent(const ui::PlatformEvent& event) override;
   uint32_t DispatchEvent(const ui::PlatformEvent& event) override;
 
+  // views::DeviceScaleFactorObserver:
+  void OnDeviceScaleFactorChanged() override;
+
   static void UpdateDeviceScaleFactorForTest();
 
  private:
@@ -68,10 +73,15 @@ class VIEWS_EXPORT DesktopScreenX11 : public display::Screen,
   // 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_;
@@ -90,12 +100,14 @@ class VIEWS_EXPORT DesktopScreenX11 : public display::Screen,
   // 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);
 };