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

ui/base/x/x11_util.cc

Index: ui/base/x/x11_util.cc
diff --git a/ui/base/x/x11_util.cc b/ui/base/x/x11_util.cc
index db9af3ce741f6e1342726fe1ef11cf4f291f8f3e..476a19e88584e54d96708dba65e17007a61ea538 100644
--- a/ui/base/x/x11_util.cc
+++ b/ui/base/x/x11_util.cc
@@ -1420,11 +1420,19 @@ void ChooseVisualForWindow(Visual** visual, int* depth) {
 
   if (!s_visual) {
     XDisplay* display = gfx::GetXDisplay();
-    XAtom NET_WM_CM_S0 = XInternAtom(display, "_NET_WM_CM_S0", False);
+
+    // Xvfb support 32 bit depths. But for some reasons NET_WM_CM_S0 it not set
+    // so at check for Composite extension instead.
+    int opcode = 0;
+    int eventb = 0;
+    int errorb = 0;
+    bool has_composite_ext =
+        XQueryExtension(display, "Composite", &opcode, &eventb, &errorb);
+    // XAtom NET_WM_CM_S0 = XInternAtom(display, "_NET_WM_CM_S0", False);

[piman, 2016/05/20 20:40:38]

This is not right. The Composite extension may exist, but if there's no
compositing WM (what the _NET_WM_CM_S0 selection indicates), then compositing
will not work.

 
     if (base::CommandLine::ForCurrentProcess()->HasSwitch(
             switches::kEnableTransparentVisuals) &&
-        XGetSelectionOwner(display, NET_WM_CM_S0) != None) {
+        has_composite_ext) {
       // Choose the first ARGB8888 visual
       XVisualInfo visual_template;
       visual_template.screen = 0;