aura: No shadow for transparent window.

ui/aura/window.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/aura/window.h"
 
 #include <algorithm>
 
 #include "base/logging.h"
 #include "base/stl_util.h"
@@ skipping 23 matching lines @@
 }
 
 }  // namespace
 
 Window::Window(WindowDelegate* delegate)
     : type_(client::WINDOW_TYPE_UNKNOWN),
       delegate_(delegate),
       parent_(NULL),
       transient_parent_(NULL),
       id_(-1),
+      transparent_(false),
       user_data_(NULL),
       stops_event_propagation_(false),
       ignore_events_(false) {
 }
 
 Window::~Window() {
   if (layer_.get())
     layer_->set_delegate(NULL);
 
   // Let the delegate know we're in the processing of destroying.
@@ skipping 39 matching lines @@
   DCHECK(transient_children_.empty());
 
   FOR_EACH_OBSERVER(WindowObserver, observers_, OnWindowDestroyed(this));
 }
 
 void Window::Init(ui::Layer::LayerType layer_type) {
   layer_.reset(new ui::Layer(layer_type));
   layer_->SetVisible(false);
   layer_->set_delegate(this);
   UpdateLayerName(name_);
+  layer_->SetFillsBoundsOpaquely(!transparent_);
 
   RootWindow::GetInstance()->WindowInitialized(this);
 }
 
 void Window::SetType(client::WindowType type) {
   // Cannot change type after the window is initialized.
   DCHECK(!layer());
   type_ = type;
 }
 
 void Window::SetName(const std::string& name) {
   name_ = name;
 
   if (layer())
     UpdateLayerName(name_);
 }
 
+void Window::SetTransparent(bool transparent) {
+  // Cannot change transparent flag after the window is initialized.
+  DCHECK(!layer());
+  transparent_ = transparent;
+}
+
 ui::Layer* Window::AcquireLayer() {
   return layer_.release();
 }
 
 void Window::Show() {
   SetVisible(true);
 }
 
 void Window::Hide() {
   SetVisible(false);
@@ skipping 465 matching lines @@
                                         parent_->children().end(),
                                         this);
   for (++i; i != parent_->children().end(); ++i) {
     if ((*i)->StopsEventPropagation())
       return true;
   }
   return false;
 }
 
 }  // namespace aura