Add Plumbing for WM_DPICHANGED

ui/views/widget/desktop_aura/desktop_window_tree_host_win.cc

Index: ui/views/widget/desktop_aura/desktop_window_tree_host_win.cc
diff --git a/ui/views/widget/desktop_aura/desktop_window_tree_host_win.cc b/ui/views/widget/desktop_aura/desktop_window_tree_host_win.cc
index fd8de8f35884f4fe7935cc83f5a7190b1427118b..de96b6309b1c3847fbd2af2aa5ba4acf8cb8148a 100644
--- a/ui/views/widget/desktop_aura/desktop_window_tree_host_win.cc
+++ b/ui/views/widget/desktop_aura/desktop_window_tree_host_win.cc
@@ -940,6 +940,15 @@ void DesktopWindowTreeHostWin::HandleWindowSizeChanged() {
   }
 }
 
+void DesktopWindowTreeHostWin::HandleWindowScaleFactorChanged(
+    float window_scale_factor) {
+  if (compositor()) {
+    compositor()->SetScaleAndSize(
+        window_scale_factor,
+        message_handler_->GetClientAreaBounds().size());
+  }
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // DesktopWindowTreeHostWin, private: