[cros] Add support for transparent background in sign in screen.

chrome/browser/chromeos/login/webui_login_view.cc

Index: chrome/browser/chromeos/login/webui_login_view.cc
diff --git a/chrome/browser/chromeos/login/webui_login_view.cc b/chrome/browser/chromeos/login/webui_login_view.cc
index cdff0ea83d3acc507251ecafdac05b4c96d70a2f..3480c7f8113e4780daaabdbf0a6b83c99bf5f730 100644
--- a/chrome/browser/chromeos/login/webui_login_view.cc
+++ b/chrome/browser/chromeos/login/webui_login_view.cc
@@ -8,11 +8,13 @@
 #include "ash/system/tray/system_tray.h"
 #include "base/bind.h"
 #include "base/callback.h"
+#include "base/command_line.h"
 #include "base/i18n/rtl.h"
 #include "base/utf_string_conversions.h"
 #include "base/values.h"
 #include "chrome/browser/chromeos/accessibility/accessibility_util.h"
 #include "chrome/browser/chromeos/cros/cros_library.h"
+#include "chrome/browser/chromeos/login/base_login_display_host.h"
 #include "chrome/browser/chromeos/login/proxy_settings_dialog.h"
 #include "chrome/browser/chromeos/login/webui_login_display.h"
 #include "chrome/browser/profiles/profile_manager.h"
@@ -21,11 +23,14 @@
 #include "chrome/browser/ui/views/ash/chrome_shell_delegate.h"
 #include "chrome/browser/ui/webui/chromeos/login/oobe_ui.h"
 #include "chrome/common/chrome_notification_types.h"
+#include "chrome/common/chrome_switches.h"
 #include "chrome/common/render_messages.h"
 #include "chromeos/dbus/dbus_thread_manager.h"
 #include "chromeos/dbus/session_manager_client.h"
 #include "content/public/browser/notification_service.h"
+#include "content/public/browser/render_view_host.h"
 #include "content/public/browser/render_view_host_observer.h"
+#include "content/public/browser/render_widget_host_view.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/browser/web_ui.h"
 #include "ui/gfx/rect.h"
@@ -203,6 +208,22 @@ void WebUILoginView::UpdateWindowType() {
 void WebUILoginView::LoadURL(const GURL & url) {
   webui_login_->LoadInitialURL(url);
   webui_login_->RequestFocus();
+
+  CommandLine* command_line = CommandLine::ForCurrentProcess();
+  // Only enable transparency on sign in screen, not on lock screen.
+  if (BaseLoginDisplayHost::default_host() &&
+      command_line->HasSwitch(switches::kEnableNewOobe)) {
+    // TODO(nkostylev): Use WebContentsObserver::RenderViewCreated to track
+    // when RenderView is created.
+    // Use a background with transparency to trigger transparency in Webkit.
+    SkBitmap background;
+    background.setConfig(SkBitmap::kARGB_8888_Config, 1, 1);
+    background.allocPixels();
+    background.eraseARGB(0x00, 0x00, 0x00, 0x00);
+    content::RenderViewHost* host =
+        wrapper_->web_contents()->GetRenderViewHost();
+    host->GetView()->SetBackground(background);
+  }
 }
 
 content::WebUI* WebUILoginView::GetWebUI() {