Run ContentMain in a browser_test's browser process. This removes duplication of code in the browse…

ui/views/test/ui_controls_factory_desktop_aurax11.cc

 // Copyright 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 <X11/keysym.h>
 #include <X11/Xlib.h>
 
 // X macro fail.
 #if defined(RootWindow)
 #undef RootWindow
@@ skipping 296 matching lines @@
 
   // Input-only window used for events.
   ::Window x_window_;
 
   DISALLOW_COPY_AND_ASSIGN(UIControlsDesktopX11);
 };
 
 }  // namespace
 
 UIControlsAura* CreateUIControlsDesktopAura() {
+  // The constructor of UIControlsDesktopX11 needs XInitThreads to be called.
+  XInitThreads();
   return new UIControlsDesktopX11();
 }
 
 }  // namespace test
 }  // namespace views