Add app.window.alphaEnabled() and onAlphaEnabledChanged.

chrome/browser/ui/views/apps/chrome_native_app_window_views_win.cc

Index: chrome/browser/ui/views/apps/chrome_native_app_window_views_win.cc
diff --git a/chrome/browser/ui/views/apps/chrome_native_app_window_views_win.cc b/chrome/browser/ui/views/apps/chrome_native_app_window_views_win.cc
index d13b495c8295d617b2aaf36e6d530d0452c5ccb6..0e91836552ab6cbee983dd657505a034b6604d2f 100644
--- a/chrome/browser/ui/views/apps/chrome_native_app_window_views_win.cc
+++ b/chrome/browser/ui/views/apps/chrome_native_app_window_views_win.cc
@@ -194,3 +194,7 @@ void ChromeNativeAppWindowViewsWin::UpdateShelfMenu() {
   // Note that an empty jumplist must still be committed to clear all items.
   jumplist_updater.CommitUpdate();
 }
+
+bool ChromeNativeAppWindowViewsWin::CanHaveAlphaEnabled() const {
+  return ui::win::IsAeroGlassEnabled();

[tapted, 2014/07/14 03:30:24]

You could also use widget()->ShouldWindowContentsBeTransparent();

Sadly (I think) it returns `false` on ChromeOS

[jackhou1, 2014/07/14 04:51:03]

ShouldWindowContentsBeTransparent is meant for native frames that have
Aero-style transparency, e.g. browser windows where the tabs are mildly
transparent. I think it's the same mechanism used to get transparent backgrounds
on Aero, but the logic isn't the same, so it's probably better to have a
different method for CanHaveAlphaEnabled.

+}