Fix SetShape (SetAlphaShape) to allow Null regions (+ tests).

ui/views/widget/desktop_aura/desktop_window_tree_host_x11.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.
 
 #include "ui/views/widget/desktop_aura/desktop_window_tree_host_x11.h"
 
 #include <X11/extensions/shape.h>
 #include <X11/extensions/XInput2.h>
 #include <X11/Xatom.h>
 #include <X11/Xregion.h>
@@ skipping 477 matching lines @@
     NOTIMPLEMENTED();
     return gfx::Rect(0, 0, 10, 10);
   }
 
   return gfx::Rect(x, y, width, height);
 }
 
 void DesktopWindowTreeHostX11::SetShape(gfx::NativeRegion native_region) {
   if (window_shape_)
     XDestroyRegion(window_shape_);
-  custom_window_shape_ = true;
-  window_shape_ = gfx::CreateRegionFromSkRegion(*native_region);
+  custom_window_shape_ = false;
+  window_shape_ = NULL;
+
+  if (native_region) {
+    custom_window_shape_ = true;
+    window_shape_ = gfx::CreateRegionFromSkRegion(*native_region);
+    delete native_region;
+  }
   ResetWindowRegion();
-  delete native_region;
 }
 
 void DesktopWindowTreeHostX11::Activate() {
   if (!window_mapped_)
     return;
 
   X11DesktopHandler::get()->ActivateWindow(xwindow_);
 }
 
 void DesktopWindowTreeHostX11::Deactivate() {
@@ skipping 1390 matching lines @@
   if (linux_ui) {
     ui::NativeTheme* native_theme = linux_ui->GetNativeTheme(window);
     if (native_theme)
       return native_theme;
   }
 
   return ui::NativeTheme::instance();
 }
 
 }  // namespace views