MacViews: Implement BridgedNativeWidget::OnDeviceScaleFactorChanged function.

ui/views/widget/native_widget_mac.mm

Index: ui/views/widget/native_widget_mac.mm
diff --git a/ui/views/widget/native_widget_mac.mm b/ui/views/widget/native_widget_mac.mm
index 812f730c92434641fcdc5a2b6acdbef70aaaf1c3..bcf2efc83fd6d25218239bdadafb32e9daebb5a9 100644
--- a/ui/views/widget/native_widget_mac.mm
+++ b/ui/views/widget/native_widget_mac.mm
@@ -480,7 +480,8 @@ bool NativeWidgetMac::IsFullscreen() const {
 }
 
 void NativeWidgetMac::SetOpacity(unsigned char opacity) {
-  NOTIMPLEMENTED();
+  if (bridge_ && bridge_->layer())
+    bridge_->layer()->SetOpacity(opacity / 255.0);

[tapted, 2015/12/17 22:38:20]

I don't know if this is correct. E.g. DesktopWindowTreeHostX11::SetOpacity(..)
uses X11 methods to change the opacity.

On Mac, we probably want to do

[GetNativeWindow() setAlphaValue:opacity / 255.0];

Let's move this to another CL - I might need to play with it a bit (and it will
need a test too :)

[Andrey Kraynov, 2015/12/18 13:51:59]

OK, I reverted my changes in this file.

 }
 
 void NativeWidgetMac::SetUseDragFrame(bool use_drag_frame) {