Make DesktopWindowTreeHostX11::ShouldWindowContentsBeTransparent() relies on argb visual flag

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 98f99f4ca391096ad4998e798bce674d3774eeb1..8e8c65f96a7e6d6229fa961a7f625eb0d6f6dfd6 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
@@ -781,7 +781,8 @@ bool DesktopWindowTreeHostX11::ShouldUseNativeFrame() const {
 }
 
 bool DesktopWindowTreeHostX11::ShouldWindowContentsBeTransparent() const {
-  return false;
+  // Ensure consistency with SetWindowTransparency().
+  return use_argb_visual_;

[sadrul, 2016/06/13 15:13:17]

DesktopWindowTreeHostWin::ShouldWindowContentsBeTransparent() returns
ShouldUseNativeFrame() here. Any reason to not want that here too? i.e. this
should check both ShouldUseNativeFrame() && use_argb_visual_?

[Julien Isorce Samsung, 2016/06/13 15:53:20]

I think it should not rely on ShouldUseNativeFrame().
DesktopWindowTreeHostX11::SetWindowTransparency() does not rely on it whereas
DesktopWindowTreeHostWin::SetWindowTransparency() does.
But one could argue that DesktopWindowTreeHostX11::SetWindowTransparency() is
wrong too.

In any case your remark made me realized that I should also update
IsTranslucentWindowOpacitySupported() and made
DesktopWindowTreeHostX11::ShouldWindowContentsBeTransparent() relies on it.

 }
 
 void DesktopWindowTreeHostX11::FrameTypeChanged() {