Add app.window.alphaEnabled() and onAlphaEnabledChanged.

This allows an app to determine whether a window created with
"transparent_background" will work as expected.

This also allows the app to detect when "transparent_background" might
stop working, e.g. when Windows changes from Aero to Classic.

This also fixes the bug where "transparent_background" windows
created in Classic render as black rectangles.

BUG=260810

Review URL: https://codereview.chromium.org/375183002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@284026 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 18 insertions, 4 deletions

diff --git a/apps/ui/native_app_window.h b/apps/ui/native_app_window.h
index cde4c1d..fd0cc26 100644
--- a/apps/ui/native_app_window.h
+++ b/apps/ui/native_app_window.h
@@ -87,6 +87,10 @@ class NativeAppWindow : public ui::BaseWindow,
   virtual void SetContentSizeConstraints(const gfx::Size& min_size,
                                          const gfx::Size& max_size) = 0;
 
+  // Returns false if the underlying native window ignores alpha transparency
+  // when compositing.
+  virtual bool CanHaveAlphaEnabled() const = 0;
+
   virtual ~NativeAppWindow() {}
 };
 
diff --git a/apps/ui/views/native_app_window_views.cc b/apps/ui/views/native_app_window_views.cc
index 62b941d..da84d8a 100644
--- a/apps/ui/views/native_app_window_views.cc
+++ b/apps/ui/views/native_app_window_views.cc
@@ -27,14 +27,12 @@ NativeAppWindowViews::NativeAppWindowViews()
       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()));
@@ -53,6 +51,10 @@ NativeAppWindowViews::~NativeAppWindowViews() {
   web_view_->SetWebContents(NULL);
 }
 
+void NativeAppWindowViews::OnCanHaveAlphaEnabledChanged() {
+  app_window_->OnNativeWindowChanged();
+}
+
 void NativeAppWindowViews::InitializeWindow(
     AppWindow* app_window,
     const AppWindow::CreateParams& create_params) {
@@ -260,7 +262,8 @@ void NativeAppWindowViews::OnWidgetActivationChanged(views::Widget* widget,
 
 void NativeAppWindowViews::RenderViewCreated(
     content::RenderViewHost* render_view_host) {
-  if (transparent_background_) {
+  if (app_window_->requested_transparent_background() &&
+      CanHaveAlphaEnabled()) {
     content::RenderWidgetHostView* view = render_view_host->GetView();
     DCHECK(view);
     view->SetBackgroundOpaque(false);
@@ -398,4 +401,8 @@ void NativeAppWindowViews::SetContentSizeConstraints(
   size_constraints_.set_maximum_size(max_size);
 }
 
+bool NativeAppWindowViews::CanHaveAlphaEnabled() const {
+  return widget_->IsTranslucentWindowOpacitySupported();
+}
+
 }  // namespace apps
diff --git a/apps/ui/views/native_app_window_views.h b/apps/ui/views/native_app_window_views.h
index bdebfde..917feca 100644
--- a/apps/ui/views/native_app_window_views.h
+++ b/apps/ui/views/native_app_window_views.h
@@ -52,6 +52,9 @@ class NativeAppWindowViews : public NativeAppWindow,
   void Init(AppWindow* app_window,
             const AppWindow::CreateParams& create_params);
 
+  // Signal that CanHaveTransparentBackground has changed.
+  void OnCanHaveAlphaEnabledChanged();
+
   views::Widget* widget() { return widget_; }
 
   void set_window_for_testing(views::Widget* window) { widget_ = window; }
@@ -156,6 +159,7 @@ class NativeAppWindowViews : public NativeAppWindow,
   virtual gfx::Size GetContentMaximumSize() const OVERRIDE;
   virtual void SetContentSizeConstraints(const gfx::Size& min_size,
                                          const gfx::Size& max_size) OVERRIDE;
+  virtual bool CanHaveAlphaEnabled() const OVERRIDE;
 
   // web_modal::WebContentsModalDialogHost implementation.
   virtual gfx::NativeView GetHostView() const OVERRIDE;
@@ -177,7 +181,6 @@ class NativeAppWindowViews : public NativeAppWindow,
   scoped_ptr<SkRegion> draggable_region_;
 
   bool frameless_;
-  bool transparent_background_;
   bool resizable_;
   apps::SizeConstraints size_constraints_;