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 586d36ddd81e4636a72c8d4fdd2745dd260045cd..161562a0d22751c72ef9d5643d2e8f17c58a15ba 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
@@ -784,7 +784,7 @@ bool DesktopWindowTreeHostX11::ShouldUseNativeFrame() const {
 }
 
 bool DesktopWindowTreeHostX11::ShouldWindowContentsBeTransparent() const {
-  return false;
+  return IsTranslucentWindowOpacitySupported();
 }
 
 void DesktopWindowTreeHostX11::FrameTypeChanged() {
@@ -940,7 +940,7 @@ bool DesktopWindowTreeHostX11::IsAnimatingClosed() const {
 }
 
 bool DesktopWindowTreeHostX11::IsTranslucentWindowOpacitySupported() const {
-  return false;
+  return use_argb_visual_;
 }
 
 void DesktopWindowTreeHostX11::SizeConstraintsChanged() {
@@ -1148,7 +1148,9 @@ void DesktopWindowTreeHostX11::InitX11Window(
     attribute_mask |= CWBorderPixel;
     swa.border_pixel = 0;
 
-    use_argb_visual_ = true;
+    // A compositing manager is required to support transparency.
+    XAtom NET_WM_CM_S0 = XInternAtom(xdisplay_, "_NET_WM_CM_S0", False);

[sadrul, 2016/06/24 03:55:13]

Use atom_cache_.GetAtom("_NET_WM_CM_S0") instead

[Julien Isorce Samsung, 2016/06/24 05:25:19]

Done.

+    use_argb_visual_ = XGetSelectionOwner(xdisplay_, NET_WM_CM_S0) != None;
   }
 
   bounds_in_pixels_ = ToPixelRect(params.bounds);