Add app.window.alphaEnabled() and onAlphaEnabledChanged.

apps/ui/views/native_app_window_views.cc

 // Copyright 2014 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 "apps/ui/views/native_app_window_views.h"
 
 #include "apps/app_window.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "content/public/browser/render_view_host.h"
 #include "content/public/browser/render_widget_host_view.h"
 #include "content/public/browser/web_contents.h"
 #include "extensions/common/draggable_region.h"
 #include "third_party/skia/include/core/SkRegion.h"
 #include "ui/gfx/path.h"
 #include "ui/views/controls/webview/webview.h"
 #include "ui/views/widget/widget.h"
 #include "ui/views/window/non_client_view.h"
 
 #if defined(USE_AURA)
 #include "ui/aura/window.h"
 #endif
 
 namespace apps {
 
 NativeAppWindowViews::NativeAppWindowViews()
     : app_window_(NULL),
       web_view_(NULL),
       widget_(NULL),
       frameless_(false),
-      transparent_background_(false),
       resizable_(false) {}
 
 void NativeAppWindowViews::Init(AppWindow* app_window,
                                 const AppWindow::CreateParams& create_params) {
   app_window_ = app_window;
   frameless_ = create_params.frame == AppWindow::FRAME_NONE;
-  transparent_background_ = create_params.transparent_background;
   resizable_ = create_params.resizable;
   size_constraints_.set_minimum_size(
       create_params.GetContentMinimumSize(gfx::Insets()));
   size_constraints_.set_maximum_size(
       create_params.GetContentMaximumSize(gfx::Insets()));
   Observe(app_window_->web_contents());
 
   widget_ = new views::Widget;
   InitializeWindow(app_window, create_params);
 
@@ skipping 205 matching lines @@
                                                      bool active) {
   app_window_->OnNativeWindowChanged();
   if (active)
     app_window_->OnNativeWindowActivated();
 }
 
 // WebContentsObserver implementation.
 
 void NativeAppWindowViews::RenderViewCreated(
     content::RenderViewHost* render_view_host) {
-  if (transparent_background_) {
+  if (app_window_->RequestedTransparentBackground() &&
+      CanHaveTransparentBackground()) {
     content::RenderWidgetHostView* view = render_view_host->GetView();
     DCHECK(view);
     view->SetBackgroundOpaque(false);
   }
 }
 
 void NativeAppWindowViews::RenderViewHostChanged(
     content::RenderViewHost* old_host,
     content::RenderViewHost* new_host) {
   OnViewWasResized();
@@ skipping 117 matching lines @@
 gfx::Size NativeAppWindowViews::GetContentMaximumSize() const {
   return size_constraints_.GetMaximumSize();
 }
 
 void NativeAppWindowViews::SetContentSizeConstraints(
     const gfx::Size& min_size, const gfx::Size& max_size) {
   size_constraints_.set_minimum_size(min_size);
   size_constraints_.set_maximum_size(max_size);
 }
 
+bool NativeAppWindowViews::CanHaveTransparentBackground() const {
+  return true;

[Wez, 2014/07/09 22:03:30]

So by default we're assuming that Views can always support transparency, unless
the platform-specific impl overrides this?

[jackhou1, 2014/07/10 03:04:18]

It looks like we use ChromeNativeAppWindowViews on CrOS and Linux. This logic
should probably live in the respective *TreeHost.

I'm not really sure what would be the idiomatic way to do this in views. Maybe
something like:
NativeAppWindowViews::CanHaveAlphaEnabled()
  calls views::Widget::CanHaveAlphaEnabled()
    calls WindowTreeHost::CanHaveAlphaEnabled()
      implemented by AppWindowDesktopWindowTreeHostWin?

[Wez, 2014/07/11 17:14:10]

Looks plausible, but I'm no expect on views/Aura.

[jackhou1, 2014/07/14 03:08:12]

benwells, any advice on this?

+}
+
+void NativeAppWindowViews::CanHaveTransparentBackgroundChanged() {
+  app_window_->OnNativeWindowChanged();

[Wez, 2014/07/09 22:03:30]

Does this fix the Classic->Aero transitions?

[jackhou1, 2014/07/10 03:04:18]

This just updates alphaEnabled in the javascript context.

[Wez, 2014/07/11 17:14:10]

Acknowledged.

+}
+
 }  // namespace apps