linux_aura: Add a flag for experimenting with ARGB windows.

ui/views/views_switches.cc

 // Copyright (c) 2013 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.
 
 #include "ui/views/views_switches.h"
 
 #include "base/command_line.h"
 
 namespace views {
 namespace switches {
 
 // Please keep alphabetized.
 
 // Specifies if a heuristic should be used to determine the most probable
 // target of a gesture, where the touch region is represented by a rectangle.
 const char kDisableViewsRectBasedTargeting[] =
     "disable-views-rect-based-targeting";
 
+#if defined(OS_LINUX) && !defined(OS_CHROMEOS)
+// When enabled, tries to get a transparent X11 visual so that we can have
+// per-pixel alpha in windows. To be removed once we've stabilized the code
+// path.
+const char kEnableTransparentVisuals[] = "enable-transparent-visuals";
+#endif
+
 bool IsRectBasedTargetingEnabled() {
 #if defined(OS_CHROMEOS) || defined(OS_WIN)
   return !CommandLine::ForCurrentProcess()->
       HasSwitch(kDisableViewsRectBasedTargeting);
 #else
   return false;
 #endif
 }
 
 }  // namespace switches
 }  // namespace views