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

ui/views/widget/native_widget_aura.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/native_widget_aura.h"
 
 #include "base/bind.h"
 #include "base/strings/string_util.h"
 #include "third_party/skia/include/core/SkRegion.h"
 #include "ui/aura/client/aura_constants.h"
@@ skipping 420 matching lines @@
     window_->parent()->StackChildAtTop(window_);
 }
 
 void NativeWidgetAura::StackBelow(gfx::NativeView native_view) {
   if (window_ && window_->parent() &&
       window_->parent() == native_view->parent())
     window_->parent()->StackChildBelow(window_, native_view);
 }
 
 void NativeWidgetAura::SetShape(gfx::NativeRegion region) {
-  // No need for this. Just delete and ignore.
-  delete region;
+  if (window_)
+    window_->layer()->SetAlphaShape(make_scoped_ptr(region));
+  else
+    delete region;
 }
 
 void NativeWidgetAura::Close() {
   // |window_| may already be deleted by parent window. This can happen
   // when this widget is child widget or has transient parent
   // and ownership is WIDGET_OWNS_NATIVE_WIDGET.
   DCHECK(window_ ||
          ownership_ == Widget::InitParams::WIDGET_OWNS_NATIVE_WIDGET);
   if (window_) {
     window_->SuppressPaint();
@@ skipping 699 matching lines @@
   l10n_util::AdjustUIFont(&(ncm.lfCaptionFont));
   base::win::ScopedHFONT caption_font(CreateFontIndirect(&(ncm.lfCaptionFont)));
   return gfx::FontList(gfx::Font(caption_font));
 #else
   return gfx::FontList();
 #endif
 }
 
 }  // namespace internal
 }  // namespace views