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

ui/base/x/x11_util.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file defines utility functions for X11 (Linux only). This code has been
 // ported from XCB since we can't use XCB on Ubuntu while its 32-bit support
 // remains woefully incomplete.
 
 #include "ui/base/x/x11_util.h"
 
@@ skipping 1402 matching lines @@
       << " (" << request_str << ")";
 }
 
 #if !defined(OS_CHROMEOS)
 void ChooseVisualForWindow(Visual** visual, int* depth) {
   static Visual* s_visual = NULL;
   static int s_depth = 0;
 
   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;
 
       int visuals_len;
       gfx::XScopedPtr<XVisualInfo[]> visual_list(XGetVisualInfo(
           display, VisualScreenMask, &visual_template, &visuals_len));
       for (int i = 0; i < visuals_len; ++i) {
         // Why support only 8888 ARGB? Because it's all that GTK+ supports. In
         // gdkvisual-x11.cc, they look for this specific visual and use it for
@@ skipping 31 matching lines @@
   if (depth)
     *depth = s_depth;
 }
 #endif
 
 // ----------------------------------------------------------------------------
 // End of x11_util_internal.h
 
 
 }  // namespace ui