Linux UI: Dynamically respond to changes in the scale factor

ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc

Index: ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc
diff --git a/ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc b/ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc
index 1414ba2b760f7f74b9b46760140480fd749f78c3..33c7a1c1b4b71dc1261fee545f580ec9021f7a1a 100644
--- a/ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc
+++ b/ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc
@@ -165,13 +165,16 @@ DesktopWindowTreeHostX11::DesktopWindowTreeHostX11(
       has_pointer_focus_(false),
       modal_dialog_counter_(0),
       close_widget_factory_(this),
-      weak_factory_(this) {}
+      weak_factory_(this) {
+  display::Screen::GetScreen()->AddObserver(this);
+}
 
 DesktopWindowTreeHostX11::~DesktopWindowTreeHostX11() {
   window()->ClearProperty(kHostForRootWindow);
   wm::SetWindowMoveClient(window(), NULL);
   desktop_native_widget_aura_->OnDesktopWindowTreeHostDestroyed(this);
   DestroyDispatcher();
+  display::Screen::GetScreen()->RemoveObserver(this);
 }
 
 // static
@@ -1289,6 +1292,26 @@ void DesktopWindowTreeHostX11::OnCursorVisibilityChangedNative(bool show) {
   // the same tap-to-click disabling here that chromeos does.
 }
 
+////////////////////////////////////////////////////////////////////////////////
+// DesktopWindowTreeHostX11, display::DisplayObserver implementation:
+
+void DesktopWindowTreeHostX11::OnDisplayAdded(
+    const display::Display& new_display) {}
+
+void DesktopWindowTreeHostX11::OnDisplayRemoved(
+    const display::Display& old_display) {}
+
+void DesktopWindowTreeHostX11::OnDisplayMetricsChanged(
+    const display::Display& display,
+    uint32_t changed_metrics) {
+  if ((changed_metrics & DISPLAY_METRIC_DEVICE_SCALE_FACTOR) &&
+      display::Screen::GetScreen()->GetDisplayNearestWindow(window()).id() ==
+          display.id()) {
+    OnHostResizedInPixels(bounds_in_pixels_.size());
+    ResetWindowRegion();
+  }
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // DesktopWindowTreeHostX11, private: