Add support for transparent background API

apps/app_window.cc

Index: apps/app_window.cc
diff --git a/apps/app_window.cc b/apps/app_window.cc
index a48f79df4f241a52c3bdc92e57ebd6bf043e91a1..cc5bf1cbd76335ca50859d4698e9e62d8b47fde7 100644
--- a/apps/app_window.cc
+++ b/apps/app_window.cc
@@ -155,13 +155,14 @@ AppWindow::CreateParams::CreateParams()
     : window_type(AppWindow::WINDOW_TYPE_DEFAULT),
       frame(AppWindow::FRAME_CHROME),
       has_frame_color(false),
-      transparent_background(false),
+      alpha_enabled(false),
       creator_process_id(0),
       state(ui::SHOW_STATE_DEFAULT),
       hidden(false),
       resizable(true),
       focused(true),
-      always_on_top(false) {}
+      always_on_top(false) {
+}
 
 AppWindow::CreateParams::~CreateParams() {}
 
@@ -238,7 +239,8 @@ AppWindow::AppWindow(BrowserContext* context,
       fullscreen_types_(FULLSCREEN_TYPE_NONE),
       show_on_first_paint_(false),
       first_paint_complete_(false),
-      cached_always_on_top_(false) {
+      cached_always_on_top_(false),
+      cached_alpha_enabled_(false) {
   extensions::ExtensionsBrowserClient* client =
       extensions::ExtensionsBrowserClient::Get();
   CHECK(!client->IsGuestSession(context) || context->IsOffTheRecord())
@@ -277,6 +279,8 @@ void AppWindow::Init(const GURL& url,
   if (new_params.state == ui::SHOW_STATE_FULLSCREEN)
     new_params.always_on_top = false;
 
+  cached_alpha_enabled_ = new_params.alpha_enabled;
+
   native_app_window_.reset(delegate_->CreateNativeAppWindow(this, new_params));
 
   if (new_params.hidden) {
@@ -726,6 +730,10 @@ void AppWindow::SetAlwaysOnTop(bool always_on_top) {
 
 bool AppWindow::IsAlwaysOnTop() const { return cached_always_on_top_; }
 
+bool AppWindow::AlphaEnabled() const {
+  return cached_alpha_enabled_;
+}
+
 void AppWindow::GetSerializedState(base::DictionaryValue* properties) const {
   DCHECK(properties);
 
@@ -734,6 +742,7 @@ void AppWindow::GetSerializedState(base::DictionaryValue* properties) const {
   properties->SetBoolean("minimized", native_app_window_->IsMinimized());
   properties->SetBoolean("maximized", native_app_window_->IsMaximized());
   properties->SetBoolean("alwaysOnTop", IsAlwaysOnTop());
+  properties->SetBoolean("alphaEnabled", AlphaEnabled());
   properties->SetBoolean("hasFrameColor", native_app_window_->HasFrameColor());
 
   // These properties are undocumented and are to enable testing. Alpha is